Influence of hot extrusion on microstructure and mechanical properties ofAZ31 magnesium alloy
气候的影响英语作文

Climate change is one of the most pressing global issues of our time,with farreaching implications for the environment,economy,and society.The effects of climate change are multifaceted and can be observed in various aspects of life on Earth.1.Environmental Impact:The most evident impact of climate change is on the environment.Rising temperatures have led to the melting of polar ice caps and glaciers, causing sea levels to rise.This not only threatens coastal cities and lowlying islands but also disrupts the habitats of many species,leading to a loss of biodiversity.Additionally, climate change has been linked to more frequent and severe weather events,such as hurricanes,floods,and droughts,which can devastate ecosystems and human settlements.2.Agricultural Effects:Agriculture is heavily dependent on stable climate conditions. Changes in temperature and precipitation patterns can lead to reduced crop yields, affecting food security globally.Droughts can decimate harvests,while floods can destroy crops and soil fertility.Moreover,warmer temperatures can shift the ranges of pests and diseases,complicating agricultural practices.3.Health Implications:Climate change can have direct and indirect effects on human health.Direct effects include heatrelated illnesses and deaths during heatwaves.Indirect effects are more complex and can include the spread of vectorborne diseases as warmer climates expand the habitats of diseasecarrying insects.Additionally,air quality can be affected by higher temperatures,exacerbating respiratory issues.4.Economic Consequences:The economic impacts of climate change are significant and varied.Industries such as agriculture,fisheries,and tourism are particularly vulnerable to the effects of climate change.Insurance costs may rise due to an increase in natural disasters,and infrastructure may require costly adaptations to withstand extreme weather events.On the other hand,some regions may experience economic benefits from a longer growing season or access to new shipping routes.5.Social and Political Ramifications:Climate change can exacerbate social inequalities and lead to political instability.Displacement of populations due to environmental disasters can create refugee crises,straining international relations and local resources. Additionally,competition for dwindling resources like water and arable land can lead to conflicts.6.Mitigation and Adaptation Efforts:In response to the impacts of climate change,there is a growing emphasis on mitigation and adaptation strategies.Mitigation involves reducing greenhouse gas emissions to slow the rate of climate change,while adaptation involves adjusting to the effects that are already occurring.This can include developingmore resilient infrastructure,investing in renewable energy,and implementing policies that promote sustainable development.cation and Awareness:Raising awareness about the impacts of climate change is crucial for driving societal and political cation plays a key role in informing the public about the science behind climate change,its consequences,and the steps that can be taken to mitigate its effects.8.International Cooperation:Addressing climate change requires a coordinated global response.International agreements,such as the Paris Agreement,aim to unite countries in efforts to reduce emissions and support those most vulnerable to climate change impacts.In conclusion,the impacts of climate change are widespread and interconnected, affecting every aspect of life on Earth.It is essential that individuals,communities,and nations work together to mitigate these effects and adapt to the changes that are already underway.。
不同预处理对热风干燥山药片品质特性及微观结构的影响

谭宏渊,凌玉钊,黄丽琪,等. 不同预处理对热风干燥山药片品质特性及微观结构的影响[J]. 食品工业科技,2023,44(20):43−52.doi: 10.13386/j.issn1002-0306.2022110328TAN Hongyuan, LING Yuzhao, HUANG Liqi, et al. Effects of Different Pretreatment on the Quality Characteristics and Microstructure of Hot Air Dried Yam Slices[J]. Science and Technology of Food Industry, 2023, 44(20): 43−52. (in Chinese with English abstract). doi: 10.13386/j.issn1002-0306.2022110328· 研究与探讨 ·不同预处理对热风干燥山药片品质特性及微观结构的影响谭宏渊1,2,凌玉钊1,2,黄丽琪1,2,熊光权2,乔 宇2, *,魏凌云1, *(1.武汉工程大学环境生态与生物工程学院,湖北武汉 430205;2.湖北省农业科学院农产品加工与核农技术研究所,湖北武汉 430064)摘 要:为比较不同干燥预处理对山药品质及微观结构的影响,以新鲜山药为原料,采用高压静电场、超高压和冷冻3种方式对切片后的山药进行预处理,利用低场核磁共振技术及干燥特性揭示干燥前后山药片内部的水分状态、分布及含量情况,分析山药片的微观结构、色泽、复水比、纤维素含量等特性的变化。
结果表明,冷冻处理对山药微观结构的破坏虽最为严重,但干燥时间最短,160 min 时水分比即可降为0.1以下;高压静电场预处理对山药片微观结构破坏程度低于其它处理方式,山药中原果胶及纤维素等细胞壁成分含量显著(P <0.05)更高,分别为11.91%和14.65%,且干燥后山药收缩较小,复水比也高于其它方式,为3.53;超高压预处理能够较好地保留山药的风味物质,且使干燥的山药白度值显著(P <0.05)提升,较干燥前提高35.10%。
作者姓名:卢滇楠

附件6作者姓名:卢滇楠论文题目:温敏型高分子辅助蛋白质体外折叠的实验和分子模拟研究作者简介:卢滇楠,男,1978年4月出生, 2000年9月师从清华大学化工系生物化工研究所刘铮教授,从事蛋白质体外折叠的分子模拟和实验研究,于2006年1月获博士学位。
博士论文成果以系列论文形式集中发表在相关研究领域的权威刊物上。
截至2007年发表与博士论文相关学术论文21篇,其中第一作者SCI论文9篇(有4篇IF>3),累计他引20次(SCI检索),EI收录论文14篇(含双收),国内专利1项。
中文摘要引言蛋白质体外折叠是重组蛋白质药物生产的关键技术,也是现代生物化工学科的前沿领域之一,大肠杆菌是重要的重组蛋白质宿主体系,截止2005年FDA批准的64种重组蛋白药物中有26种采用大肠杆菌作为宿主体系,目前正在研发中的4000多种蛋白质药物中有90%采用大肠杆菌为宿主表达体系。
但由于大肠杆菌表达系统缺乏后修饰体系使得其生产的目标蛋白质多以无生物学活性的聚集体——包涵体的形式存在,在后续生产过程中需要对其进行溶解,此时蛋白质呈无规伸展链状结构,然后通过调整溶液组成诱导蛋白质发生折叠形成具有预期生物学活性的高级结构,这个过程就称之为蛋白质折叠或者复性,由于该过程是在细胞外进行的,又称之为蛋白质体外折叠技术。
蛋白质体外折叠技术要解决的关键问题是避免蛋白质的错误折叠以及形成蛋白质聚集体。
目前本领域的研究以具体技术和产品折叠工艺居多,折叠过程研究方面则多依赖宏观的结构和性质分析如各类光谱学和生物活性测定等,在研究方法上存在折叠理论、分子模拟与实验研究结合不够的问题,这些都不利于折叠技术的发展和应用。
本研究以发展蛋白质新型体外折叠技术为目标,借鉴蛋白质体内折叠的分子伴侣机制,提出以智能高分子作为人工分子伴侣促进蛋白质折叠的新思路,即通过调控高分子与蛋白质分子的相互作用,1)诱导伸展态的变性蛋白质塌缩形成疏水核心以抑制蛋白质分子间疏水作用所导致的聚集,2)与折叠中间态形成多种可逆解离复合物,丰富蛋白质折叠的途径以提高折叠收率。
Mg-9Gd-4Y-2Zn-0.5Zr_镁合金的微观组织与性能研究

精 密 成 形 工 程第16卷 第1期24 JOURNAL OF NETSHAPE FORMING ENGINEERING2024年1月收稿日期:2023-09-16 Received :2023-09-16基金项目:江西省教育厅项目(190751);江西省教育厅科学技术研究项目(GJJ211440)Fund :Jiangxi Provincial Department of Education Project (190751); Science and Technology Research Project of Jiangxi Pro-vincial Department of Education (GJJ211440)引文格式:娄崟崟, 杨初斌, 文春花, 等. Mg-9Gd-4Y-2Zn-0.5Zr 镁合金的微观组织与性能研究[J]. 精密成形工程, 2024, 16(1): 24-32.LOU Yinyin, YANG Chubin, WEN Chunhua, et al. Microstructure and Properties of Mg-9Gd-4Y-2Zn-0.5Zr Magnesium Alloy[J]. Journal of Netshape Forming Engineering, 2024, 16(1): 24-32. *通信作者(Corresponding author ) Mg-9Gd-4Y-2Zn-0.5Zr 镁合金的微观组织与性能研究娄崟崟,杨初斌*,张小联,文春花,韩宝军,何人桂(赣南师范大学 镁合金材料工程技术研究中心,江西 赣州 341000)摘要:目的 研究挤压比对热挤压制备的Mg-9Gd-4Y-2Zn-0.5Zr (VW94)镁合金微观组织、拉伸性能和抗腐蚀性的影响,并揭示挤压比对组织和性能演变的影响机制。
方法 用挤压比为16和35的热挤压工艺制备了Mg-9Gd-4Y-2Zn-0.5Zr (VW94)镁合金,通过光镜(OM )、X 射线衍射仪(XRD )、扫描电子显微镜(SEM )等手段表征并分析了不同挤压比下的微观组织,进一步通过拉伸测试和电化学测试评估合金的力学性能和腐蚀速率,并通过SEM 表征断口形貌和腐蚀形貌,分析其断裂方式和腐蚀机制。
写火山爆发的科普英语作文

写火山爆发的科普英语作文Volcanic Eruptions: A Natural Phenomenon。
Volcanic eruptions are one of the most fascinating and powerful natural events on Earth. They occur when molten rock, known as magma, rises to the surface through cracks in the Earth's crust. This magma, along with gases and other materials, is then expelled into the air, creating a volcanic eruption. In this article, we will explore the causes, effects, and types of volcanic eruptions.There are several factors that contribute to volcanic eruptions. The primary cause is the movement of tectonic plates, which make up the Earth's crust. When two plates collide or separate, it creates a weak point where magma can escape. Additionally, the composition of the magma plays a significant role. Magma with a high viscosity, or thickness, tends to trap gases and build up pressure, leading to explosive eruptions. On the other hand, magma with low viscosity flows more easily, resulting in less explosive eruptions.The effects of volcanic eruptions can be both immediate and long-term. In the short term, eruptions can cause devastating consequences. The release of ash, gases, and pyroclastic materials can lead to the destruction of nearby communities and infrastructure. Ash clouds can also disrupt air travel and pose health risks to humans and animals. Furthermore, volcanic eruptions can trigger secondary hazards such as landslides, tsunamis, and lahars (mudflows).Over the long term, volcanic eruptions play a crucial role in shaping the Earth's surface. The lava and ash released during eruptions create new landforms, such as volcanic mountains and islands. The minerals and nutrients in volcanic soil also make it highly fertile, providing ideal conditions for agriculture. However, the location of volcanic activity can also have adverse effects on the environment. For example, volcanic gases can contribute to air pollution and climate change.There are several types of volcanic eruptions, each characterized by different characteristics and levels of explosiveness. The most common type is called a Strombolian eruption, named after the volcano Stromboli in Italy. These eruptions are relatively mild and consist of bursts of lava and gas. Another type is the Vulcanian eruption, which is more explosive and produces dense ash clouds and pyroclastic flows.One of the most dangerous types of eruptions is the Plinian eruption. Named after the Roman historian Pliny the Younger, these eruptions are characterized by a tall column of ash and gas that can reach several kilometers into the atmosphere. The eruption of Mount Vesuvius in 79 AD, which buried the city of Pompeii, is a famous example of a Plinian eruption.In conclusion, volcanic eruptions are a natural phenomenon that results from the movement of tectonic plates and the release of magma from the Earth's interior. They have both immediate and long-term effects on the environment and can be highly destructive. Understanding the causes, effects, and types of volcanic eruptions is crucial for scientists and communities living in volcanic regions. By studying and monitoring volcanic activity, we can better prepare for and mitigate the impact of these powerful natural events.。
负压状态窄缝通道乙二醇水溶液传热特性

化工进展Chemical Industry and Engineering Progress2023 年第 42 卷第 S1 期负压状态窄缝通道乙二醇水溶液传热特性赵晨1,苗天泽2,张朝阳3,洪芳军1,汪大海1(1 上海交通大学机械与动力工程学院,上海 200240;2 清华大学先进高功率微波重点实验室,北京100084;3上海交通大学巴黎卓越工程师学院,上海 200240)摘要:高效、紧凑的换热方式需求日益增大,具有高度方向速度梯度大的窄缝通道成为最有前景的方式之一。
本文以质量分数为55%的乙二醇水溶液为工质,针对钛窄缝通道在负压工况进行流动沸腾换热实验。
实验在质量流率750~2000kg/(m 2·s)、饱和温度为80~90℃、入口温度60~70℃的条件下进行。
结果表明,钛需要更高的热流密度激活大量成核点,从而其过冷沸腾起始点(ONB )前后平均换热系数h 基本不变;质量流量对于ONB 和沸腾充分发展阶段的平均换热系数影响很大;在高过冷度时,沸腾充分发展阶段,钛窄缝通道换热性能对于入口温度不敏感;提高进口温度降低过冷度可以极大提高平均换热系数,70℃条件下平均换热系数在沸腾充分发展阶段可以提高65%;背压对于换热性能的影响主要在沸腾充分发展阶段,背压越低平均换热系数越大。
关键词:微通道;乙二醇水溶液;负压;气液两相流;流动沸腾;传热中图分类号:TK124 文献标志码:A 文章编号:1000-6613(2023)S1-0148-10Heat transfer characteristics of ethylene glycol aqueous solution in slitchannel under negative pressureZHAO Chen 1,MIAO Tianze 2,ZHANG Chaoyang 3,HONG Fangjun 1,WANG Dahai 1(1 School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China; 2 Advanced High PowerMicrowave Key Laboratory, Tsinghua University, Beijing 100084, China; 3 Ecole d'ingenieurs Paris, Shanghai Jiao TongUniversity, Shanghai 200240, China)Abstract: The increasing demand for efficient and compact methods of heat transfer has generated interest in the utilization of a narrow channel with a significant velocity gradient along its height, thus presenting substantial potential. This research study focused on investigating the heat transfer phenomena in a flow boiling system that employs a narrow slot channel made of titanium under negative pressure conditions. The experimental analysis employed a designated working fluid, namely an ethylene glycol aqueous solution with a mass concentration of 55%. The experimentation was conducted under specific operational parameters, encompassing a mass flow rate spanning from 750kg/(m²·s) to 2000kg/(m²·s), a saturation temperature within the range of 80℃ to 90℃, and an inlet temperature ranging from 60℃ to 70℃. The findings of the study revealed that the activation of a substantial quantity of nucleation sites in titanium necessitated an elevated heat flux. Consequently, this phenomenon maintained the average heat transfer coefficient (h ) in a state of relative constancy both prior to and subsequent to the onset of nucleate boiling (ONB). The heat flux required to start of ONB and the mean heat transfer coefficient during the研究开发DOI :10.16085/j.issn.1000-6613.2023-1153收稿日期:2023-07-09;修改稿日期:2023-08-28。
食用碱添加对不同冷冻杂粮面团品质特性的影响

杜文凯,苏同超,胡向华,等. 食用碱添加对不同冷冻杂粮面团品质特性的影响[J]. 食品工业科技,2023,44(24):54−62. doi:10.13386/j.issn1002-0306.2023010143DU Wenkai, SU Tongchao, HU Xianghua, et al. Effect of Edible Alkali Addition on the Quality Characteristics of Different Frozen Multigrain Doughs[J]. Science and Technology of Food Industry, 2023, 44(24): 54−62. (in Chinese with English abstract). doi:10.13386/j.issn1002-0306.2023010143· 研究与探讨 ·食用碱添加对不同冷冻杂粮面团品质特性的影响杜文凯,苏同超*,胡向华,曾 洁,高海燕,王洋洋,田佳楠,马明君,周海旭(河南科技学院食品学院,河南新乡 453003)摘 要:为了研究食用碱添加量对不同冷冻杂粮(小麦、荞麦、玉米、绿豆)面团品质的影响,本文设计了0%、1%、2%、3%、4%、5%(以100 g 冷冻杂粮面团为基准)食用碱添加量分别加入到小麦面团、荞麦面团、玉米面团、绿豆面团中,在−30 ℃条件下冷冻8 h ,在−18 ℃的条件下冷冻1 d ,然后在25 ℃下解冻30 min 。
然后分别测定冷冻面团的失水率、持水率、pH 、质构特性、水分分布以及利用扫描电子显微镜(SEM )对冷冻面团表面网络结构和蛋白质结构的变化进行研究。
结果表明,食用碱添加量与冷冻面团的失水率呈负相关,可以显著(P <0.05)影响冷冻面团的pH ;在食用碱添加量为4%时,各个冷冻杂粮面团的弹性达到最大值,小麦面团、荞麦杂粮面团、玉米杂粮面团、绿豆杂粮面团的A 21分别达到48.189±1.509、45.652±2.202、43.585±2.472、43.743±1.155,说明食用碱可以抑制水分迁移,进而保持良好的持水性,且能有效改善冷冻杂粮面团面筋蛋白网络结构和品质,进一步提高冷冻杂粮面团品质。
Effect of heat treatment on microstructure and

Effect of heat treatment on microstructure and mechanical properties of extruded ZM61 magnesium alloyF.G.Qi1,2,D.F.Zhang*1,2,Z.T.Zhu1,2,X.X.Xu1,2and G.L.Shi3The effects of T5and T6heat treatments on the microstructure and mechanical properties of extruded Mg–6Zn–1M n alloy were investigated in the present study.The results showed that T5 and T6treatments could markedly improve the strengths of extruded ZM61alloy,and the precipitate strengthening effect of double aging was better than that of single aging.The precipitates formed in the T6treatment were much finer and more dispersive than the ones in the T5treatment,resulting in stronger precipitation strengthening effect.However,due to additional grain size refinement strengthening effect,the T5treatment could improve ductility without sacrificing strength over the T6treatment.Scanning electron microscopy observation and tensile test indicated that different cooling methods after extrusion,such as air cooling and water quenching,had no obvious influence on the microstructure and strengths of extruded and subsequent heat treated Mg–6Zn–1Mn alloys.In addition,the Mn element mainly existed as fine Mn phase particles,which were well dispersed in the matrix.Dispersed Mn particles could be found in rod-like b’1precipitates,but not in the disc shaped b’2precipitates.Keywords:Mg–Zn–Mn,Heat treatment,Precipitate,Microstructure,Mechanical propertiesIntroductionAs the lightest structure metal materials with high specific strength and stiffness,good damping capacity, excellent machinability and good castability,magnesium alloy is the most attractive material in aerospace, transportation and mobile electronics.1–4However,due to limited strength,poor formability and high cost of expensive composition elements used,the application of magnesium alloy is still limited.5–8Therefore,it is pressing to develop some new wrought magnesium alloys with high strength and low cost.Mg–Zn alloys are the most widely used wrought magnesium alloy.9,10 Owing to the problems with hot shortness and coarse and uneven grain size in binary Mg–Zn alloy,commer-cially Mg–Zn alloys are always grain refined by the addition of Zr.11In addition,RE and Cu have been added to improve both casting characteristics and mechanical properties at elevated temperature.12–15 However,the additions of these elements also increase the alloy’s cost.Mg–6Zn–1Mn(ZM61)alloy is a new promising alloy, which is developed to meet the above requirements. Zhang et al.16,17reported that the mechanical properties of ZM61alloy with solution and aging treatment can achieve the level of the commercial wrought ZK60A alloy.16Recently,Park et al.18,19investigated the effect of the Al addition on the microstructure and tensile properties of ZM61alloy and found that ZM61–1Al alloy exhibited excellent tensile properties as a result of refined precipitates by Al addition.More recently,the microstructure and mechanical properties of the Mg–x Zn–1Mn alloy have been reported.20According to the reports,the Mg–6Zn–1Mn(ZM61)alloy had the best comprehensive mechanical properties.It is well known that strengthening via grain size control is particularly effective in magnesium alloys because of the higher Hall–Petch coefficient.21,22For the most part of Mg–Zn series alloys,solution treatment after plastic deformation can significantly coarsen the grain so that the mechanical properties of T6aged alloys are worse than T5aged alloys.23,24It was reported that the hardness and strength of extruded ZK60alloy under T5condition were higher than those under T6condition because the second phase precipitated during the aging process wasfiner and more dispersive under T5 condition than that under T6condition.23The micro-structure and mechanical properties of forged ZK60-Y alloy under various heat treatments have been reported.24The results showed that T5treated alloy had superior tensile strength and plasticity compared with T4and T6treated alloys.1College of Materials Science and Engineering,Chongqing University, Chongqing400045,China2National Engineering Research Center for Magnesium Alloys,Chongqing University,Chongqing400044,China3State Key Laboratory for Fabrication and Processing of Non-Ferrous Metals,General Research Institute for Non-Ferrous Metals,Beijing 100088,China*Corresponding author,email zhangdingfei@1426ß2012Institute of Materials,Minerals and MiningPublished by Maney on behalf of the InstituteReceived15May2012;accepted27July2012DOI10.1179/1743284712Y.0000000095Materials Science and Technology2012VOL28NO12Although some researches on the microstructure of ZM61alloy have been carried out,no systematical study was focused on heat treatment of extruded ZM61alloy.In the present study,the effect of T5and T6heat treatment on the microstructure and mechanical proper-ties of extruded ZM61alloy were investigated.This study also aims to investigate the relationship between precipitations and mechanical properties and to opti-mise the heat treatment parameters.ExperimentalThe nominal composition (in wt-%)of the alloy used in the present study is Mg–6Zn–1Mn.The experimental alloy was prepared from commercial high purity Mg (.99?9%),Zn (.99?95%)and Mg–4?1%Mn master alloy by melting in an electrical resistance furnace under a SO 2z CO 2protective gas and then casting them into a steel mould.The actual composition of alloy was analysed by XRF-800CCDE X-ray fluorescence spec-trometer,and the result is Mg–5?9300Zn–1?0200Mn–0?0094Al–0?0049Fe–0?0058Si–0?0015Cu–0?0005Ni (wt-%).Experimental detail is schematically presented in Fig.1.First,cast ingots were homogenised at 330u C for 24h with air cooling.Before the ingots were extruded,the ingots and extrusion die were heated to 420u C for 90min.To study the effect of the preheating treatment on the microstructure,small samples for microstructure observation were also heat treated with the same heating regime and then quenched in water to retain the high temperature microstructures.Then,the homogenised ingots were hot extruded into bars 16mm in diameter at 420u C.The extrusion ratio was 25:1,and the ram speed was set at 3m min 21during extrusion.To investigate the effect of cooling methods after extrusion on the microstructure and mechanical proper-ties of extruded and subsequent heat treated alloys,different cooling methods of air cooling and water quenching were used.Following this,the samples were given T5or T6heat treatment.In the case of T5treatment,the extruded bars were merely single aged (180u C for 16h)and double aged (90u C for 24h followed by 180u C for 16h)respectively.In the case of T6treatment,the extruded bars were solution treated at 420u C for 2h followed by water quenching and thenimmediately single aged (180u C for 16h)and double aged (90u C for 24h followed by 180u C for 16h)respectively.Cylindrical tensile samples,50mm in gauge length and 5mm in gauge diameter,were machined from the extruded and aged bars along the extrusion direction.Tensile tests were conducted on a Sans CMT-5105electronic universal testing machine at room tempera-ture with a displacement rate of 3mm min 21.Each test condition was repeated at least three times for repeat-ability and accuracy.Microstructure was observed by an optical microscope (NEOPHOT30),a scanning electron microscope (SEM)(TESCAN VEGAII)equipped with an Oxford INCA Energy 350energy dispersive X-ray (EDS)spectrometer.Precipitates were examined using a transmission electrical microscope (Zeiss LIBRA 200FE)operating at 200kV.Phase constitutions were determined by a Rigaku D/max 2500PC X-ray diffractometer with the use of Cu K a radiation and a scanning rate of 4u min 21.Results and discussionMicrostructure of as cast and as homogenised alloysFigure 2shows the microstructures of the as cast and as homogenised ZM61alloys.As shown in Fig.2a and c ,the as cast microstructure of the experiment alloy consists of a -Mg matrix and eutectic compounds.The eutectic com-pounds are Mg 7Zn 3phase by X-ray diffraction (XRD)analysis as shown in Fig.3a .Mn exists as pure a -Mn.The average grain size of as cast alloy is y 160m m.After homogenisation at 330u C for 24h,some of the eutectic compounds in the grain boundary dissolve into the matrix as shown in Fig.2b and d .Figure 3b shows the XRD pattern of the as homogenised ZM61alloy.It is clearly seen that the peaks of the Mg 7Zn 3phase become weaker,and some peaks of the MgZn 2phase are detected,indicating that MgZn 2is precipitated during the Zn diffusion.Microstructure of extruded and solution treated alloysThe preheating microstructures of ZM61alloy at 420u C for 90min and quenching in water is shown in Fig.4.1Extrusion and heat treatment scheduleQi et al.Effect of heat treatment on extruded ZM61magnesium alloyMaterials Science and Technology 2012VOL28NO121427After homogenisation at 330u C for 2h (Fig.3),some of the Mg–Zn eutectic compounds in the grain boundary cannot dissolve completely into the matrix.These undissolved compounds,however,are found to dissolve into the matrix during the preheating of the ingots before extrusion,indicating a low thermal stability of these Mg–Zn compounds.Microstructural changes after hot extrusion with air cooling and water quenching are shown in Fig.5a and b .Owing to the deformation and the occurrence of dynamic recrystallisation during the hot extrusion process,equiaxed grain microstructure is formed,and the average grain size is y 9m m.The effect of preheating treatment at 420u C on the microstructure has already been studied.As is stated above,almost all the eutectic compounds are solutionised into the matrix aftera ,b optical micrographs;c ,d SEM images2Microstructures of a ,c as cast and b ,d as homogenised ZM61alloys3X-ray diffraction patterns of a as cast and b as homo-genised ZM61alloys 4Preheating microstructure of ZM61alloy at 420u C for90min and quenching in waterQi et al.Effect of heat treatment on extruded ZM61magnesium alloy1428Materials Science and Technology 2012VOL28NO12homogenisation and preheating treatment at 420u C.Therefore,little second phase particles are retained,and the complete dynamic recrystallisation happens during extrusion at 420u C,resulting in equiaxed grain.In addition,it is found that there is no difference on the microstructure of extruded ZM61alloys with different cooling methods including air cooling and water quenching.Figure 5c presents an SEM image of ZM61alloy after solution treatment at 420u C for 2h.The average grain size of the solution treated is y 25m m.The dynamic recrystallised grains of the investigated alloy grew up sharply,and all the broken particles dissolved into the matrix,resulting in a high Zn solid solution concentration.The phase evolution was further determined by XRD analysis.Figure 6shows XRD patterns of the extruded and solution treated samples.It is obvious that the diffraction patterns of extruded specimens mainly contain a -Mg matrix,Mn and MgZn 2phase.However,the weak diffraction patterns of the MgZn 2precipitates in the extruded alloy significantly broadened.According to the Scherrer formula,25peak broadening qualitatively illustrates a decrease in grain5a ,b images (SEM)of ZM61alloy after extrusion with a air cooling and b water cooling and c SEM and d TEM imagesof ZM61alloy after solution treated at 420u C for 2h6X-ray diffraction patterns of ZM61alloy after extrusionwith a air cooling and b water cooling and c X-ray dif-fraction patterns of ZM61alloy after solution treated at 420u C for 2hQi et al.Effect of heat treatment on extruded ZM61magnesium alloyMaterials Science and Technology 2012VOL28NO121429size in the corresponding phase,implying that some nanosized MgZn 2precipitates form during the cooling after extrusion.After solution treatment at 420u C for 2h,the diffraction patterns show that the MgZn 2phase disappears,which suggests that a uniform solid–solution structure is produced,as shown in Fig.5c .In addition,the detailed microstructure inside the a -Mg after solution treatment is shown in Fig.5d .From the TEM image,only one spherical phase can be observed.No other phases are detected after solution treatment.Based on the XRD result and previous studies,19,20we can preliminarily conclude that the spherical phase is pure Mn particle.Microstructure of aged alloysFigure 7shows the SEM images of ZM61alloy in the T5(single aging)and T6(single aging)state.Since the SEM images of single aged alloys are very similar to those of double aged alloys,one of them is displayed here.By comparing Figs.5a and 7a ,the alloy in the T5(single aging)state shows the similar microstructure to the extruded alloy.The average grain size of the T5aged alloy is y 11m m.As shown in Figs.5c and 7c ,there is little difference on microstructure between T4treated and T6aged alloys under the SEM observation.In fact,many nanosized Mg–Zn precipitates that are formed during the aging treatment are observed in Fig.8c .Figure 7a and b shows the SEM microstructures of ZM61alloy in the T5(single aging after extrusion with air cooling and water quenching respectively)state.It can be found that there is no obvious change on microstructures under SEM between the two.It is well known that magnesium metal and its alloys have high thermal diffusivity,high thermal conductivity and high efficiency of heat release.26The diameter of extruded bars is only 16mm,so the extruded alloys with air cooling and water quenching have same macrostruc-tures.In addition,the average grain size of the T5treated alloy is much finer than that of the T6treated alloy due to high temperature solution treatment in the latter.Figure 8shows TEM images of ZM61alloy in the T5and T6treatment states.It is observed that two kinds of precipitates formed during aging treatments.Based on previous studies,27–30we can conclude that the two precipitates are rod-like b ’1and disc shaped b ’2phases respectively.The interface between b ’1and the matrix is coherent,while semicoherent between b ’2and the matrix.b ’1phases,which formed as rods with their long axis parallel to the [0001]a direction of the a -Mg matrix,can act as a more enormous impediment to the motion of dislocations than b ’2formed as plates on (0001)a ,as reported in previous studies.27–30In all samples,the precipitates after double aging (Fig.8b and d )are much finer and more dispersed than those after single aging (Fig.8a and c ).It is because the nanosized G.P.zones,which formed during the preaging at 90u C for 24h,could provide more effective nuclei for b ’1phase during the second aging.On the other hand,b ’1and b ’2precipitates in T5treated alloys are relatively less than those in T6states.This is because the Zn solid solubility in T6states is slight higher than that in T5states,and a few broken particles formed after extrusion are grown and retained after T5treatment.In addition,it is observed that many spherical phases are well dispersed in the matrix,which are found in thea ,b T5(single aging after extrusion with a air cooling and b water quenching);c T6(single aging)7Images (SEM)of ZM61alloy at different single agingtreatments conditionsQi et al.Effect of heat treatment on extruded ZM61magnesium alloy1430Materials Science and Technology 2012VOL28NO12rod-like b ’1precipitates but not found in disc shaped b ’2precipitates.As mentioned above,the spherical phase for the solution treated alloy is initially speculated to Mn.Figure 9shows a high angle annular dark field scanning TEM image of ZM61alloy in the T6(double aging)state and the typical EDS result of a spherical phase.It can be seen that the spherical phase is pure a -Mn particle,which can further illustrate the existence form of Mn element.As mentioned above,there are only Mn particles observed in the solution treated alloy,suggesting that Mn particles have a higher thermal stability than MgZn bined with Figs.5d and 8,it is observed that some rod-like b ’1precipitates nucleate on the pre-existing Mn particles.Mechanical properties of ZM61alloyThe mechanical properties of ZM61alloy in different conditions are shown in Fig.10.Figure 10a shows the effect of heat treatment conditions on mechanical properties of extruded ZM61alloy.On one hand,it is noted that double aging could result in a significantincrease in tensile and yield strength as compared with single aging.This is because large amount of G.P.zones,which could act as nuclei for b ’1precipitates,formed during the pre-aging at 90u C for 24h.Therefore,it results in finer and more dispersed b ’1and b ’2precipitates in the second step aging at 180u C for 16h.On the other hand,it is interesting to note that there is no obvious difference in the strengths between T5and T6treated alloys,and the elongations of T5treated alloys are higher than T6treated alloys,as shown in Fig.10a .The strengths of the aged alloys are determined by the combined contributions of grain size refinement strengthening and precipitation strengthening.As the precipitate size is finer and the volume fraction and distribution is larger in the T6treated sample,the precipitation strengthening effect is stronger.However,the average grain size of T5treated alloys is much finer than that of T6treated alloy due to high temperature solution treatment of T6treatment.Therefore,T5treatment can improve ductility without sacrificinga T5(single aging);b T5(double aging);c T6(single aging);d T6(double aging)8Images (TEM)of ZM61alloy at different aging treatments conditionsQi et al.Effect of heat treatment on extruded ZM61magnesium alloyMaterials Science and Technology 2012VOL28NO121431strength over T6treatment due to additional grain size refinement strengthening effect,although precipitation strengthening effect is marginally lower compared to T6treated samples.Figure 10b shows the effect of cooling methods after extrusion on the mechanical properties of extruded and subsequent heat treated alloys.There is no difference in strengths of extruded and subsequent heat treated ZM61alloys with different cooling methods including air cooling and water quenching.As mentioned above,magnesium alloys have high thermal diffusivity,high thermal conductivity and high efficiency of heat release,so the extruded and heat treated ZM61alloys with air cooling and water quenching have same microstructures observed under a scanning electron microscope.There-fore,there are no difference in strengths of extruded and subsequent heat treated ZM61alloys with air cooling and water quenching.ConclusionsThe effects of T5and T6heat treatments on the microstructure and mechanical properties of extruded Mg–6Zn–1Mn alloy have been investigated.The main conclusions can be summarised as follows.1.T5and T6treatments can markedly improve the strengths of extruded ZM61alloy,and T5treatment can improve ductility without sacrificing strength over T6treatment.The precipitates formed in T6treatment are finer and more dense than in T5treatment,resulting in stronger precipitation strengthening effect.However,the grain size of T5treated alloy is much finer compared to T6treated alloy.2.Scanning electron microscopy observation and tensile test reveal that different cooling methods after extrusion,such as air cooling and water quenching,have no obvious influence on microstructure and strengths of extruded and subsequent heat treated ZM61alloys.3.Mn element mainly exists as fine Mn phase particle,which are well dispersed in the matrix.Some rod-like b ’1precipitates nucleate on the Mn dispersoid particles.AcknowledgementsThis work was sponsored by the National Great Theoretic Research Project (grant no.2007CB613700),the National Science and Technology Support Project (grant no.2011BAE22B01-3),the National Natural Science Foundation of China (no.50725413),the International Cooperation Project (grant nos.2010DFR50010and 2008DFR50040),the Chongqing Science and Tech-nology Project (grant no.2010CSTC-HDLS)and the Fundamental Research Funds for the Central Universities (grant no.CDJXS10132202).ReferencesD.Eliezer,E.Aghion andF.H.Froes:‘Magnesium science,technology and applications’,Adv.Perform.Mater.,1998,5,(3),201–212.X.Cao,M.Jahazi,J.P.Immarigeon and W.Wallace:‘A review of laser welding techniques for magnesium alloys’,J.Mater.Process.Technol.,2006,171,(2),188–204.9a high angle annular dark field scanning TEM image ofZM61alloy after T6(double aging)and b corresponding EDS results of point A 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