Study On Design Of High Performance Al-Si-Cu-Mg Alloy

With the aim of designing high-performance semi-solid Al-Si-Cu-Mg alloys, and base on the influence of alloying elements and grain size on microstructures, the content of the alloying elements is that silicon's content is less than 12.6%, copper and magnesium less than 5.65% and 1.0%, respectively. Thus, by means of multi-scale numerical simulation, the microstructure of aluminium alloys with different silicon, copper and magnesium content in near-liquidus casting was investigated. The results could provide guidance to the semi-solid alloy design and technical optimization of Al-Si-Cu-Mg alloy.The thermodynamics parameters of Al-Si-Cu-Mg alloy were calculated using the Thermo-Calc software. The model of temperature field, concentration field, nucleation and grain growth was established for the semi-continuous casting process. By coupling the calculations of thermal field on macro scale with that of grain growth on micro scale, it was simulated the evolution of microstructures of the Al-Si-Cu-Mg alloys under different conditions. The relationships of the element content, casting velocity and pouring temperature were obtained. Thus the optimal composition and technical conditions for semi-solid forming were obtained.It is found from the simulation that the microstructure of the alloy by near-liquidus casting is much better than conventional casting. The lower the pouring temperature approachs to the liquidus, the better the microstructure is. The casting velocity has great influence on the microstructures. The grains become fine and round with decrease of the casting velocity, and reach the best at 0.002m/s. The optimal content of silicon's is 7%, copper 3%～4% and the magnesium 0.4%～0.8%. The simulatied result is consistent with the experiment. Investigations show that the designed alloy Al-7%Si-4%Cu-0.6%Mg will be superior to ZL107 in the properties of metal forming and application. It is expected that the strength of Al-7%Si-4%Cu-0.6%Mg will be 320-450MPa, the rate of elongation 3.0-4.5% and hardness great than 105HB.It is shown from the study of Al-Si-Cu-Mg alloy that multiscale simulation is an effective method to design the semisolid Al-Si-Cu-Mg alloys and optimize the technical parameters, which provide a new idea to the semisolid alloy design.