Effect of grain refining, mould material and pouring temperature on the microstructural characteristics of AA6063 aluminum alloy feedstocks produced using low superheat casting

摘要

In the present investigation, feedstocks of AA6063 wrought aluminum alloy, with a thixotropic microstructure, were prepared using low superheat casting (LSC). The effects of pouring temperature, mould material and the grain refining using Al-5%Ti-1%B master alloy on the microstructural characteristics of AA6063 wrought Al alloy were studied. An optimization of the aforementioned parameters was carried out using Taguchi's approach. Moreover, the analysis of variance (ANOVA) statistical approach was carried out to clarify the level of significance of the parameters and their optimum combination. The results revealed that the grain refining has the greatest influence on both the average grain size and shape factor of the primary α-Al grains. Feedstocks poured using the grain refiner exhibited lower size and higher shape factor of α-Al grains than those poured without grain refining. Increasing the pouring temperature slightly increases the average size while reduces the average shape factor of the primary α-Al grains. Feedstocks poured in the copper mould exhibited the lowest average size and highest average shape factor of primary α-Al when compared with feedstocks poured in low carbon steel and stainless steel moulds. The optimum microstructural characteristics suitable for thixoforming was exhibited for grain refined AA6063 feedstocks poured in the copper mould at 665℃.