稀土La对AZ31变形镁合金组织及性能的影响

发布时间：2018-04-05 10:53

  本文选题：AZ31镁合金　切入点：La　出处：《合肥工业大学》2017年硕士论文

【摘要】：镁合金作为最轻的轻质金属结构材料,商业应用前景相当广阔,被誉为“21世纪绿色结构材料”。然而对于密排六方晶体结构的镁合金,由于其室温塑性差,成型困难和绝对强度低等问题,严重制约镁合金的发展。本文采用室温拉伸、维氏硬度及电化学腐蚀测试方法,金相(optical microstructure,OM),X射线衍射(X-ray,XRD)、能谱扫描(energy spectrum analysis,EDS)、电子显微镜(SEM)等分析手段,研究了稀土La改性、冷轧工艺和再结晶退火工艺等因素对AZ31镁合金的微观组织结构、力学性能以及耐蚀性能的影响规律。取得的主要研究结论和成果如下(1)设计了5组合金成分,La的加入量分别为0.2%、0.3%、0.4%、0.6%和0.9%。研究表明:添加微量La,能够细化AZ31铸态组织,获得具有细小等轴形貌的晶粒;同时细化了原始粗大的第二相Mg17Al12,产生热稳定性良好、细小针状的析出相Al11La3。当La的含量为0.6%时,合金铸态组织晶粒大小约为40μm,晶粒最细小,合金力学性能最优。另外,添加La能提高合金的抗腐蚀性能,当La含量为0.4%时合金耐腐蚀性能较优,此时时效态变形合金(总加工率约为75%)的静态腐蚀深度为10mm/a,且随着La的继续增加,抗腐蚀性能降低,当La含量为0.6%时,其静态腐蚀深度为17.9mm/a,仍优于商用AZ31镁合金(静态腐蚀深度约为60mm/a)。(2)设计了3组冷轧工艺,变形量分别为10%、20%和30%,以探究冷轧工艺参数对AZ31-0.6La合金组织与性能的影响规律。研究表明:合金临界冷轧压下量为30%,超过30%,合金组织将会碎裂。当合金的冷轧量为10%时,冷轧过后合金内部产生了大量位错和孪晶,经过240℃×1h+200℃×24h热处理后,合金能获得较优的力学性能和抗腐蚀性能,其时效态(合金总加工率约为75%)抗拉强度与屈服强度、延伸率和静态腐蚀深度分别为:340MPa/240MPa、25%、1.02mm/a。(3)通过设计再结晶退火工艺的温度(240℃、280℃和320℃)和时间(t=5、10…180min),研究再结晶退火工艺对AZ31-0.6La合金经10%冷轧后的组织与性能的影响规律。研究表明:合金板材经240℃×2.5h退火处理后,发生完全再结晶,获得晶粒最细小且均匀的合金组织。(4)结合显微硬度测试(AZ31-0.6La冷轧量5%、10%和15%,240℃、280℃和320℃,t=5、10…180min)和Arrhenius方程,确定了AZ31镁合金发生静态再结晶的激活能,建立了AZ31镁合金的静态再结晶动力学方程和晶粒尺寸模型。
[Abstract]:As the lightest light metal structure material, magnesium alloy has a broad prospect of commercial application and is praised as "green structural material in the 21st century".However, the development of magnesium alloys with dense hexagonal crystal structure is seriously restricted because of its poor room temperature plasticity, difficult forming and low absolute strength.In this paper, rare earth La modification was studied by means of room temperature stretching, Vickers hardness and electrochemical corrosion test, X-ray diffraction X ray diffraction (X ray diffraction), energy spectrum analysis (EDS), electron microscopy (SEM), etc.Effects of cold rolling and recrystallization annealing on microstructure, mechanical properties and corrosion resistance of AZ31 magnesium alloy.The main conclusions and results obtained are as follows: 1) the addition amount of La in 5 combinations is 0.20.30.30.40% and 0.9% respectively.The results show that the as-cast microstructure of AZ31 can be refined by adding a small amount of La, and the grains with fine equiaxed morphology can be obtained, and the coarse second phase Mg17Al12 is refined, resulting in good thermal stability and fine needle-like precipitated phase Al11La3.When the content of La is 0.6, the grain size of the as-cast alloy is about 40 渭 m, the grain size is the smallest, and the mechanical properties of the alloy are the best.In addition, the addition of La can improve the corrosion resistance of the alloy. When La content is 0.4, the corrosion resistance of the alloy is better, and the static corrosion depth of the aging deformed alloy (total processing rate is about 75mm / a) is 10 mm / a, and increases with the increase of La content.When La content is 0.6, its static corrosion depth is 17.9 mm / a, which is still superior to commercial AZ31 magnesium alloy (the static corrosion depth is about 60 mm / a) and three groups of cold rolling process have been designed.The deformation amounts are 10% and 30% respectively to investigate the effect of cold rolling process parameters on the microstructure and properties of AZ31-0.6La alloy.The results show that the critical cold rolling reduction of the alloy is 30 and above 30, the microstructure of the alloy will break.When the cold rolling amount of the alloy is 10, a large number of dislocations and twins occur inside the alloy after cold rolling. After heat treatment at 240 鈩，

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