Mg-6Al-5Zn-xCa(x=4,5,6,7)-5Gd合金的显微组织和力学性能

The microstructure and mechanical properties of Mg-6Al-5Zn-xCa（x=4,5,6,7）-5Gd alloys.

摘要:

本文研究了不同高含Ca量的Mg-6Al-5Zn-xCa(x=4,5,6,7)-5Gd合金铸态以及热处理后的显微组织和力学性能。结果表明，铸态时，随着含Ca量的增加，连续分布于晶界处的第二相β-Mg25(Al, Zn)37.5逐渐变细，呈颗粒状的Al2Gd相和块状的CaZn5相部分溶解，以更加圆润的小颗粒状相和小块状相分布在组织中，其抗拉强度和屈服强度先升高后降低，伸长率下降；固溶处理后，大部分β-Mg25(Al, Zn)37.5相逐渐溶入合金基体中，合金的强度和伸长率均显著增加，随着含Ca量的增加，固溶组织中分布更多的颗粒状相和块状相，其抗拉强度和屈服强度先升高后降低，伸长率变化不大；固溶+时效处理后，产生时效强化，时效12h后合金硬度达到峰值，随时效时间延长，硬度稍有降低，然后趋于平缓，说明合金有较优异的热稳定性。断口分析表明，随着含Ca量的增加和热处理方式的不同，合金的断裂机制有从脆性断裂向韧性断裂转变的趋势。当含Ca量为6wt%时，合金铸态断口形貌中有明显韧窝存在，热处理后，其断口形貌中韧窝数量增多，大小一致，分布趋于均匀。实验合金以Mg-6Al-5Zn-6Ca-5Gd合金经390℃/8h固溶+200℃/12h时效处理后的力学性能最佳。

Abstract:

The effects of different high content of Ca and heat treatment on microstructure and mechanical properties of the as-cast Mg-6Al-5Zn-xCa-5Gd alloys were investigated in this paper. The results indicate that with the addition of Ca content in as-cast condition, the β-Mg25(Al, Zn)37.5 phase which continuously distributes in grain boundary becomes finer. The granular Al2Gd and the block CaZn5 phase gradually dissolve in the matrix more uniformly. Hence the tensile strength and yield strength increases firstly, then decreases, and the elongation decreases all the way. After the solid solution treatment, the most of β-Mg25(Al, Zn)37.5 phase is dissolved in the matrix, and the strength and the elongation increases obviously. With the increase of Ca content, much more granular and lump phase distribute in the surface. And the ultimate tensile strength and yield strength increases firstly, then decreases, but little change has happened with the elongation. After solid solution treatment and aging treatment, the age-hardening of alloys reachs the peak at 12h. Then the hardness tends towards stability after slightly lowering, which shows that the alloy has significant thermal stability. Fracture analysis shows that with the increase of calcium and the different heat treatment, fracture mechanism of the alloys transforms from brittle to ductile. With the content of Ca increasing to 6wt%, dimples can be observed obviously. After the heat treatment, the dimples are increasing and the size of which are uniform. The mechanical properties of the alloy of Mg-6Al-5Zn-6Ca-5Gd by solid solution treatment at 390℃/8h and aging treatment at 200℃/12h get optimal performance.