半固态成形过共晶Al-Si-Cu-Mg合金短流程热处理强化机理研究

The properties of semi-solid castings can not improve obviously after traditional T6 heat treatment, which arouse attentions from the industries and institutes. While previous studies showed that mechanical properties of semi-solid Al alloys after short heat treatment increased obviously than that by traditional T6 heat treatment. Therefore, short heat treatment has wider potential application with higher efficiency and lower cost. However the strengthening mechanism of short heat treatment of Al alloys after semi-solid forming is not clear yet. The strengthening mechanism of short heat treatment hypereutectic Al-Si-Cu-Mg alloys after semi-solid forming is studied by combining with diffusion and phase transformation theory, thermodynamics and dynamics theory and solid electronic theory together. The purpose of this project is to reveal the effect of semisolid forming conditions on the heat treatment strengthening mechanism of hypereutectic Al-Si-Cu-Mg alloys. The research focused on: the effect of semi-solid forming parameters on the heat treatment behavior of hypereutectic Al-Si-Cu-Mg alloys, aging strengthening characteristics of semi-solid forming hypereutectic Al-Si-Cu-Mg alloys, and the nucleation and growth dynamics mechanism of aging precipitations of hypereutectic Al-Si-Cu-Mg alloy in different aging stages after semi-solid forming. The research aims to systematically investigate short heat treatment behavior of semi-soild forming hypereutectic Al-Si-Cu-Mg alloys and reveals the formation essence of this abnormal heat treatment behavior, which can enrich the present heat treatment theory of Al alloys. It is hopeful to provide a new way or an innovative method to make superior quality with higher efficiency, more energy saving and lower cost for high performance semi-solid forming Al castings.

半固态铸件在传统T6热处理后性能提高不明显的现象一直受到工业界的关注，而申请者前期研究发现，对半固态成形铝合金进行短流程热处理，可充分发挥铝合金半固态成形组织优势，获得优于传统T6处理的良好强化效果，这种现象表现出了高效低成本的广阔应用前景，但该现象形成的本质尚未揭示。本研究结合扩散与相变理论、热力学与动力学理论和固体电子理论，针对半固态成形过共晶Al-Si-Cu-Mg合金短流程热处理强化机理展开研究，目的是揭示半固态成形条件在合金热处理强化过程中的作用机理。为此，本项目将系统研究半固态成形参数对合金热处理行为的影响规律，分析半固态成形合金时效强化特性，掌握半固态成形条件下各强化相在析出不同阶段形核、长大的动力学机制，从而揭示半固态成形过共晶Al-Si-Cu-Mg合金短流程热处理强化行为形成的本质，可丰富铝合金热处理强化理论，也为高效节能制备高性能半固态成形铝合金件开辟一种新的途径和方法。

半固态金属成形技术是21世纪最具发展前途的近净形成形关键技术之一，在汽车、通讯、电器及航空航天等领域有广阔的应用前景。热处理是进一步提高合金力学性能的重要手段，但目前半固态成形合金热处理强化理论方面的研究成果尚显薄弱。半固态铸件在传统T6热处理后性能提高不明显的现象一直受到工业界的关注。申请者前期研究发现，对半固态成形铝合金进行短流程热处理，可充分发挥铝合金半固态成形组织优势，获得优于传统T6处理的良好强化效果，这种现象表现出了高效低成本的广阔应用前景，但该现象形成的本质尚未揭示。因此，对半固态成形合金热处理行为及其机理进行深入而全面的研究有一定的实际意义和理论价值。.本项目系统研究了半固态成形参数对合金热处理行为的影响规律，分析半固态成形合金时效强化特性，掌握半固态成形条件下各强化相在析出不同阶段形核、长大的动力学机制，从而揭示半固态成形过共晶Al-Si-Cu-Mg合金短流程热处理强化行为形成的本质。实验研究发现：随着半固态挤压的比压增加，合金组织中初生Si变得细小，分布也较为均匀。比压为600MPa时，合金力学性能较好。随着固溶时间的增加，合金组织中块状的初生Si相棱角开始变钝、变圆，条片状的共晶Si相发生颈缩、熔断及粒状化，Al2Cu相等强化相尺寸减小，合金的性能提高。固溶10h时，合金组织中Si相的单位面积个数、圆形度和平均直径达到最优，合金的力学性能达到峰值，抗拉强度为311MPa，屈服强度为291MPa，伸长率为2.20%，硬度为132.0HB；此时，合金在磨损实验中的表面磨损形貌中剥落坑较小、犁沟细小且较浅，合金的磨损量和平均摩擦系数较低，分别为2.4mg和0.3913，合金的耐磨性较好。时效1h时，合金组织中出现点状析出物Q′′相；时效8h时，合金组织中出现棒状析出物θ′相，点状析出物数量减少；时效12h时，合金组织中棒状析出物和点状析出物的数量减少。