材料工程学院金属材料力学性能（论文）
提高AZ91镁合金抗拉强度的措施
学生姓名： 学生学号： 院 （系）： 年级专业： 指导教师：
二〇一三年12月15日
目 录
1 概述·····································································································································1 2 提高AZ91镁合金抗拉强度的措施 ··························································································2
2.1 稀土合金化处理 ·························································································································2
2.1.1 添加La ·····························································································································2 2.1.2 添加Nd ·····························································································································3 2.1.3 添加Ce ·····························································································································3 2.1.4 添加微量Sr ······················································································································3 2.1.5 添加Y ·······························································································································3 2.2 热处理 ··········································································································································4
2.2.1 均匀化退火处理 ··············································································································4 2.2.2 变形镁合金T6热处理 ···································································································4 2.2.3 对挤压态AZ91镁合金热处理工艺 ·············································································4 2.2.4 在线淬火、离线固溶处理和时效处理 ········································································4 2.3 强变形高压处理 ·························································································································5
2.3.1 热挤压 ·······························································································································5 2.3.2 等径角挤压 ······················································································································5 2.3.3 往复挤压 ··························································································································5 2.3.4 六面顶压机高压处理 ······································································································6 2.4 复合处理 ······································································································································6
3 结语 ························································································································································6 参考文献 ···················································································································································7
1 概述
镁合金是目前最轻的金属结构材料，比强度和比刚度高，在航空航天及汽车工业领域有着广阔的应用前景。其中AZ91镁合金具有良好的铸造性能、力学性能以及耐腐蚀性能，而且成本低廉，因而是应用最为广泛的Mg-Al-Zn系合金之一。但由于镁是密排六方晶体结构，滑移系少，塑性加工性能较差。尤其是目前铸造AZ91镁合金产品内部组织粗大，且往往存在组织不均匀等缺陷，造成其产品性能受到制约。因此，开发适当的工艺对AZ91镁合金进行强化与改性成为重要的研究课题。
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2 提高AZ91镁合金抗拉强度的措施
2.1 稀土合金化处理
单独或复合添加稀土元素在金属中形成固溶相或在晶界偏聚，对合金的相变、显微组织有明显的影响，可以改变合金的物理性能，而且稀土元素还能够对镁合金起到净化作用。
2.1.1 添加La
对添加La的AZ91镁合金进行研究发现，La只有微量固溶在Mg中，其余的则与Al形成了Al11La3化合物。随着La加入量的增大，Al11La3以针状或团状形态析出，起到了弥散强化的作用，降低了组织的晶粒度。张金玲[1]试制出一种高强高韧镁合金试样，其抗拉强度≥190MPa，伸长率≥11%。La加入量为1.0%时，合金的硬度、室温和200℃高温抗拉强度分别比原始合金提高31.6%、26.2%和27.2%，室温和高温伸长率也分别比原始合金提高了1241%[2-3]。
2.1.2 添加Nd
王娜等[4]将Nd添加到AZ91镁合金后，Nd与Al因有较强的亲和力而形成块状的面心立方结构Al3Nd相。另外，Nd元素的加入促进等轴晶的形成，使组织细化。当Nd的加入量为0.4%时，合金的抗拉强度和伸长率表现较好。并且添加Nd使AZ91镁合金的腐蚀速率明显降低，含Nd量为1.4%的合金腐蚀速率最小，耐蚀性能较佳。
2.1.3 添加Ce
赵源华等[5-6]一定量的Ce加入AZ91镁合金后，AZ91镁合金中连续网状分布的β相变成断续的小块状弥散分布于晶界。当Ce加入量为0.69%时，合金铸态组织得到明显细化，同时有大量的针状Al4Ce相出现，此时合金综合力学性能较佳，其抗拉强度、伸长率分别比原始AZ91镁合金提高15.8%和140%。而当Ce加量为0.93%时，合金的铸态组织反而较加入量为0.69%时有粗化趋势。
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2.1.4 添加微量Sr
白星等[7-9]研究认为微量Sr能够细化AZ91合金的铸态共晶组织，块状或杆状的金属间化合物Mg17Sr2、Al4Sr相偏聚在晶界，阻碍了晶粒的生长。0.1%～0.2%的Sr添加量可提高合金的强度和韧性。当Sr含量为0.2%时，Sr的固溶强化和Al4Sr相的晶界强化等因素使合金的室温和高温抗拉强度和伸长率都有一定程度的增加。但当Sr含量为0.3%时，合金抗拉强度和塑性则都会下降。
2.1.5 添加Y
李金锋等[10-12]研究得出添加适量的Y元素后，AZ91镁合金微观组织中析出的高熔点Al2Y相能有效提高原有组织的热稳定性，从而有效提高合金的高温性能。但当Y加入量超过0.9%时，合金组织反而变得粗大，合金的力学性能开始降低。当Y添加过量时，组织中的Al2Y相容易聚集成团，造成合金组织和成分的不均匀，从而引起应力集中，导致合金抗拉强度严重下降。
2.2 热处理
热处理是通过一定的温度处理，改变材料表面或内部的金相组织结构，控制其性能的金属热加工工艺。
2.2.1 均匀化退火处理
白云[13]对AZ91镁合金经过均匀化退火处理后，粗大网状的β相溶解，冷却过程中脱溶析出。布氏硬度比铸态提高45%，抗拉强度和屈服强度分别提高36%和37%，伸长率由铸态的2%增加到6.52%。韩秋华[14]将AZ91镁合金铸锭经430℃×28h固溶时效处理后，抗拉强度和硬度分别提高29.49%和24.04%。
2.2.2 变形镁合金T6热处理
张建民等[15]对变形镁合金经T6热处理，发生热处理强化，在固溶强化的基础上析出大量β强化相，合金的强度和硬度提高，但塑性降低。经360℃压缩变形及190℃T6热处理后，抗拉强度、屈服强度及伸长率分别为351MPa、270MPa和9.86%。
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提高AZ91镁合金抗拉强度的措施
