Microstructure evolution during semi-solid powder rolling and post-treatment of 7050 aluminum alloy strips

Semi-solid powder rolling (SSPR) combines semi-solid rolling with powder rolling to prepare high-performance metallic strips. Semi-solid powders were prepared under an inert atmosphere and subsequently rolled by a powder rolling machine. Conductive cooling between the pre-heated rollers and semi-solid powders results in a rapid solidification effect that is able to process alloys with a broad freezing range. The liquid in the semi-solid powders plays an important role in the microstructure evolution, which can improve the strength of strips. The 7050 aluminum alloy strips were obtained and used to evaluate the processing parameters and strip qualities for strips up to 100 mm wide and 1.5-2 mm thick. The process of semi-solid powder rolling was described and microstructure evolution during rolling and post-treatment was analyzed. The combination mechanism of semi-solid powders during rolling was also discussed. The results show that the best liquid fraction to prepare a strip ranges from 45 to 65%. Flowing and filling of liquid (>10%), densification by rolling and recrystallization (<10%) are the three combination mechanisms of the semi-solid powders during rolling. In addition, semi-solid powder rolled strips can be processed subsequently by hot rolling with the improved micro-hardness and relative density.