Study Of SIM Solidification Process And Mechanism For Near Net Shape Casting Of Wrought Aluminum Alloys

The wrought aluminum alloys are appreciated by automobile and aerospace industry because of their excellent properties. Because of the restrictions of processing method, there was a high cost of forming wrought aluminum alloys. If the wrought alloy was formed by casting method, the production cost will be reduced. Because of the disadvantage of as-casting method, the semi-solid method was more suitable for forming wrought alloys.In this thesis,the semi-solid slurry of 2024 and 7075 alloy was prepared by a novel Self-Inoculation Method(SIM) which is with high efficiency and low energy consumption. In this work, 2024 and 7075 wrought aluminum alloys used for semi-solid processing are optimized by means of thermodynamic simulations (Pandat). And the simulation results also provide a useful guide for the experiments on semi-solid processing. A series of experiments on 2024 wrought aluminum alloys were carried out to investigate the effects of processing parameters on the semi-solid microstructure. Microstructure's formation mechanism of SIM has been studied.The results indicate that:(1) According to the calculated results of Pandat, 2024 and 7075 wrought aluminum alloys were suitable for semi-solid processing;(2) SIM is the best pouring method, and globular microstructure was developed by the multi-stream mixed cooling channel.(3) The suitable condition can increase effective nucleation rate and obtain high quality semi-solid slurry, which requires the parameters match of the melt treatment temperature (700～7300℃,2024; 690～740℃,7075),length(600mm)and angle(45°) of the cooling channel and addition of the self-inoculants(5%).(4) Semi-solid slurry with much fine and uniform primary phase particles is gained by self-inoculation method. The inoculant increases the thermal and constituional fluctuation,and plays a role of nucleation, solification acceleration during solidification of 2024 alloy. The dendrites are broken and distributed dispersedly into residual alloy liquid and form free grains.