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Phase Decomposition of Heat Resistant Magnesium Alloys Containing Heavy Rare Earth Elements and Its Control

含重稀土耐热镁合金的相分解及其控制

基本信息

批准号：
07455257
负责人：
KOJIMA Yo
金额：
$ 4.99万
依托单位：
Nagaoka University of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07455257/
关键词：
Magnesium Alloy Rare Earth Containing Alloy Phase Diagram Aging Characteristics Hot Workability Microstructural Control Corrosion Resistance High Temperature Tensile Property ミクロ組織

项目摘要

The aim of this study is to develop a new magnesium alloy which has more excellent heat and corrosion resistance than that of the conventional heat resistant aluminum and magnesium alloys that could be applicable to piston and other engine parts undergoing the highest thermal load among automobile parts. The Mg-rich portion of phase diagrams, aging characteristics, hot workability, corrosion behavior and microstructural control of magnesium alloys containing heavy rare earth elements were investigated. Finally, the alloys were hot-forged into a piston shape and their tensile properties were also evaluated. (1) The solid solubilities of heavy rare earth elements in magnesium shift largely to lower concentrations than those of Mg-Gd or -Dy binary alloys by Nd or Y addition with decreasing temperature. As a result, alloys containing Gd or Dy of more than 6% and Nd or Y of more than 3% show marked age hardening even at 250ﾟC and have higher tensile strength than the conventional magnesium … More alloys. (2) The precipitation sequences of the investigated alloys are as follows : Magnesium supersaturated solid solution* beta" (DO_<19>) *beta' (bco) *Equilibrium beta (Nd containing alloy : fcc, Y containing alloy : bcc). The remarkable age hardening is caused by the precipitation of metastable beta"-phase. The beta"-phase precipitate preferentially on the dislocations introduced by the hot rolling or hot forging and, therefore, precipitation free zone near the grain boundaries is reduced. As a result, tensile properties are enhanced by the hot working. (3) It is possible for the investigated alloys to suppress grain coarsening and to reduce the amount of remained eutectic compound by lowering the homogenizing temperature to just above the solubility limit and, therefore, to directly dieforge all specimens into a piston shape without an intermediate upset forging. Die-forged Mg-10%Gd-3%Y alloys exhibits a tensile strength of 290MPa and 0.2% proof stress of 250MPa at 250ﾟC,which are superior to those of the conventional heat resistant magnesium alloys and are more than double those of the conventional heat resistant aluminum alloys. (4) A fine Mg (OH)_2 layr is formed as the stable protective film on the surface of all investigated alloys by the additions of rare earth elements under a corrosive environment containing a chloric ion. Less

本研究的目的是开发一种比传统耐热铝镁合金具有更好的耐热性和耐腐蚀性的新型镁合金，适用于汽车零件中热负荷最大的活塞和其他发动机零件。研究了重稀土镁合金的相图富镁部分、时效特性、热加工性能、腐蚀行为和组织控制。最后，将合金热锻造成活塞形状，并对其拉伸性能进行了评价。(1)随着温度的降低，重稀土元素在镁中的固溶度随温度的降低而向镁-Gd或-Dy二元合金的低浓度方向移动。结果表明，Gd或Dy含量大于6%，Nd或Y含量大于3%的合金即使在250ﾟC也表现出显著的时效硬化，并且具有比传统的镁…更高的抗拉强度更多的合金。(2)所研究合金的析出顺序为：镁过饱和固溶体*β“(Do&lt；19&gt；)*β‘(BCO)*平衡β(含Nd合金：fcc，含Y合金：bcc)，显著的时效硬化是由亚稳β”相的析出引起的。β“相优先在热轧或热锻造引入的位错上析出，从而减少了晶界附近的析出区。结果表明，热加工提高了材料的拉伸性能。(3)通过将均匀化温度降低到略高于溶解度极限，可以抑制晶粒粗化，减少残余共晶化合物的数量，从而直接将所有试件模锻成活塞形状，而不需要中间锻造。模锻镁-10%Gd-3%Y合金在250ﾟC下的抗拉强度为290 Mpa，0.2%的抗拉强度为250 Mpa，优于常规耐热镁合金，是常规耐热铝合金的两倍多。(4)在含有氯离子的腐蚀环境中，稀土元素的加入在所有被研究合金的表面形成了一层细小的氢氧化镁保护膜。较少