论文部分内容阅读
研究了不同高含Ca量的Mg-6Al-5Zn-x Ca(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-Mg_(25)(Al,Zn)_(37.5)逐渐变细,呈颗粒状的Al_2Gd相和块状的CaZn_5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-Mg_(25)(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12 h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质量分数为6%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℃/8 h固溶+200℃/12 h时效处理后的力学性能最佳。
The microstructures and mechanical properties of Mg-6Al-5Zn-xCa (x = 4,5,6,7) -5Gd alloys with different contents of Ca and their as-cast and heat-treated alloys were studied. The results show that the as-cast second phase β-Mg_ (25) (Al, Zn) _ (37.5), which is continuously distributed at the grain boundaries, is tapered to form granular Al_2Gd phases And bulk CaZn_5 phase partially dissolved, with a more rounded small granular phase and small phase distributed in the organization, the tensile strength and yield strength first increased and then decreased, the elongation decreased; solution treatment, Most of the β-Mg_ (25) (Al, Zn) _ (37.5) phases gradually dissolved into the alloy matrix, and the strength and elongation of the alloys increased significantly. With the increase of Ca content, Of the granular phase and the bulk phase, the tensile strength and yield strength first increased and then decreased, little change in elongation; solid solution + aging treatment, resulting in aging strengthened, the alloy hardness peaked at 12 h, at any time Effective time, a slight decrease in hardness, and then tends to be gentle, indicating the alloys have excellent thermal stability. Fracture analysis shows that with the increase of Ca content and the different heat treatment methods, the fracture mechanism of alloy has the tendency to change from brittle fracture to ductile fracture. When Ca content is 6%, there are obvious dimples in the as-cast fracture morphology. After heat treatment, the number of dimples in fracture morphology increases, the size is uniform, and the distribution tends to be uniform. The mechanical properties of Mg-6Al-5Zn-6Ca-5Gd alloy after aging at 390 ℃ / 8 h + 200 ℃ / 12 h were the best.