专业英语摘要翻译

摘要

镁合金是一种性能优异的金属结构工程材料，其综合力学性能优良。含碱土元素的AZ91镁合金能够改善铸态镁合金高温力学性能差、耐腐蚀性能不足、晶粒粗大等缺点，且碱土元素相比稀土元素更具经济实惠。本文通过向AZ91镁合金基体中加入碱土元素Ca、Sr，研究挤压固溶时效工艺方案与试验合金显微组织和力学性能的变化关系，运用X衍射分析（XRD），扫描电子显微镜（SEM）和高频疲劳试验机PLG-200仪器等研究Ca和Sr组织成分、力学性能特征。

1）AZ91铸态组织组成相为α-Mg和β-Mg17Al12相，β-Mg17Al12相的存在形态为指纹状或骨骼状。AZ91中加入1%的Ca，试验合金的晶粒尺寸明显变小，而β-Mg17Al12也主要以颗粒状或小尺寸短条状弥散分布，并且在晶界形成了熔点为1079℃的化合物Al2Ca。随0.2%Sr 的加入，晶进粒的平均尺寸进一步变小。AZ91、AZ91-1.0%Ca、AZ91-1.0%Ca-0.2%Sr铸态试验合金高温抗拉强度分别为124.7MPa、116.9 MPa、135.8MPa说明复合添加1%Ca和0.2%Sr可以提高合金的高温力学性能。

2）试验合金进行热挤压变形时发生了动态再结晶，晶粒得到细化，其平均晶粒尺寸约为37um。AZ91镁合金中复合添加Ca、Sr使得合金晶粒细化，阻碍位错运动，使得合金抗拉强度提高。420℃*28h+200℃*16h达到时效峰值，析出β-Mg17Al12相最多，硬度为80.0HBS。2#试验镁合金中由于Ca的加入导致晶界处Al的浓度降低，导致峰值出现的时间延迟。时效峰值出现时间为26h，硬度为

76.7HBS。3#试验合金时效峰值时间再次延后至80h，但峰值上升为76.8HBS。

3）铸态AZ91镁合金的断裂方式为典型的脆性断裂机制，AZ91-1%Ca和AZ91-1%Ca-0.2%Sr塑性变形能力提高，镁合金拉伸断裂方式为准理面断裂，裂纹扩展区变长且出现韧窝和准解理台阶。

关键词：AZ91镁合金；钙；锶；显微组织；力学性能；疲劳裂纹

Abstract

Magnesium alloy is a kind of excellent metal structural engineering material, it’s good comprehensive mechanical properties. AZ91 magnesium alloy containing alkaline earth elements can improve the as-cast poor high temperature mechanical properties and corrosion resistance of magnesium alloys is insufficient, coarse grains and other shortcomings, and alkaline earth elements in rare earth elements is more economical. This article through to the AZ91 magnesium alloy substrate with alkaline earth elements Ca, Sr, the extrusion solid solution aging technology scheme and experimental alloy and the changes of microstructure and mechanical properties with X-ray diffraction analysis (XRD), scanning electron microscope (SEM) and high frequency fatigue tester PLG - 200 instruments such as study of Ca and Sr organization composition, the mechanical performance characteristics.

1) AZ91 as-cast organization of phase for α-Mg and β- Mg

17Al

12

phase,

the existence of theβ- Mg

17Al

12

phase morphology for fingerprints or bones.

Alloy AZ91 adding 1% of Ca, test of the grain size decreased significantly,

andβ- Mg

17Al

12

is mainly granular or small size short bars are dispersed,

and formed the melting point is 1079 ℃ in the grain boundary compound Al

2

Ca. With the addition of 0.2% Sr, crystal into the grain of the average size of further smaller. AZ91, AZ91-1.0% Ca, AZ91-1.0% Ca–0.2% Sr test alloy high temperature tensile strength were 124.7 MPa, 116.9 MPa, 135.8 MPa that compound added 1% Ca and 0.2% Sr can improve the high temperature mechanical properties of alloy.

2)test alloy during hot extrusion deformation dynamic recrystallization, grain size refinement, the average grain size of about 37 um. AZ91 magnesium alloy composite added Ca, Sr has alloy grain refinement, hinder dislocation motion, makes the alloy tensile strength increase. 420℃*28 h + 200 ℃ * 16 h peak aging and precipitation beta

Mg

17Al

12

phase most, hardness of 80.0 HBS. 2 # test of magnesium alloy in

grain boundary due to the addition of Ca ，Al concentration is reduced, cause peak time delay. Aging peak time of 26 h, hardness of 76.7 HBS. 3 # test of alloy 80 h after peak aging time delay again, but the peak increased to 76.8 HBS.

3) fracture ways of as-cast AZ91 magnesium alloy for typical brittle fracture mechanism, AZ91-1% Ca and AZ91-1%Ca-0.2% Sr plastic deformation ability enhancement, magnesium alloy tensile failure mode shall prevail plane rupture, crack extension zone longer and toughening nest and quasi cleavage stage.

Key words: AZ91 magnesium alloy; Calcium; Strontium; The microstructure; Mechanical properties; Fatigue crack