Al-Si-Fe铸造铝合金的搅拌摩擦加工组织和性能研究

Microstructure and Properties of Al-Fe-Si Alloy under Friction Stir Processing

对不同热处理状态的Al-Si-Fe铸造铝合金进行了搅拌摩擦改性,采用光学显微镜(OM)、扫描电镜(SEM)、拉伸试验机、显微硬度仪等研究了合金状态及改性后热处理对合金组织和性能的影响。结果表明:搅拌摩擦加工后合金的铸造缺陷消失,但存在明显的组织不均匀性和不对称性,源于前进侧的带状组织均匀性和细化程度均高其它区域,而铸态合金更容易获得带状组织。改性后第二相的平均长度和圆整度均大幅改善,长度最大减小90%以上,而圆整度则提高7倍以上。相比于T6态合金,铸态合金的改性效果更好,且富铁相的细化效果较共晶硅好。改性后T6热处理对富铁相的长度和圆整度均略有改善,而共晶硅略有长大,圆整度大幅提高。改性后合金的延伸率提高了4.3倍以上,而强度则与改性前合金状态相关。改性前未处理的合金强度、硬度略有提高,而改性前T6处理的合金的强度、硬度大幅降低。当铸态合金经改性后进行T6热处理,获得的组织最为均匀、细小,综合力学性能最佳。

The Al-Si-Fe cast aluminum alloys with different states were modified by friction stir processing. The effects of alloy state and heat treatment post-processing on microstructure and properties were investigated by optical microscope(OM), scanning electron microscope(SEM), tensile tester and microhardness tester. The results showed that casting defects disappeared after modification, but structural inhomogeneities and asymmetry still existed obviously. The uniformity and refinement degree of banded zone originating from advancing side were better than that of other processing zones, while as-cast alloy was easy to obtain more banded structure. The length and roundness of the second phase were greatly improved after modification, the maximum length reduction reached to 90% above and roundness increased more than 7 times. However, modification effect of second phase with as-cast state was better than that of T6 state, meanwhile the refinement effect of iron-rich phase was better than that of eutectic silicon. The length and roundness of iron-rich phase modified were improved slightly after T6 heat treatment, while length of eutectic silicon was increased slightly, and roundness was improved greatly. Elongation of alloy was improved significantly after modification, which increased more than 4.3 times compared to the substrate, while the strength was related to alloy state before processing. The strength and hardness of untreated alloy were improved slightly after modification, while the strength and hardness of the alloy treated by T6 treatment before modification were greatly reduced. Finally, the most uniform, fine microstructure and comprehensive mechanical properties were obtained by friction stir processing as-cast alloy firstly and T6 heat treatment later.