超声半固态流变挤压成形Al-20Si-2Cu-0.4Mg-1Ni合金的组织特征(英文)

通过超声振动半固态流变挤压铸造工艺制造汽车空调压缩机铝硅合金斜盘零件,研究合金的组织特征。发现在Al20Si2Cu0.4Mg1Ni合金的组织中,除了通常具有的初晶Si和α(Al)+β-Si共晶相之外,还有非平衡α(Al)颗粒或枝晶。挤压铸造过程中的较快的冷却速度而非压力是非平衡α(Al)相形成的主要原因。在半固态浆料的制备过程中,超声振动的声压作用能促进非平衡α(Al)相在共晶温度以上生成,并生长为非枝晶颗粒。超声处理的过共晶AlSi合金中的非平衡α(Al)相由共晶温度以上生成的圆形α(Al)晶粒和少量共晶温度以下生成的细小α(Al)枝晶构成。由于超声振动的作用使α(Al)基体中的Si的固溶度增加,并使初晶Si的形成温度降低,组织中初晶Si颗粒的体积分数显著降低。流变挤压斜盘中的初晶Si颗粒的平均直径和体积率分别为24.3μm和11.1%。

Microstructural characteristics of Al-20Si-2Cu-0.4Mg-1Ni alloy formed by rheo-squeeze casting after ultrasonic vibration treatment

A swash plate for air conditioning compressor of cars was formed by rheo-squeeze casting with semi-solid Al-Si alloy slurry prepared by ultrasonic vibration process, and the microstructure of this alloy was investigated. Besides the microstructures of primary Si particles and α(Al)+β-Si eutectic phases, non-equilibrium α(Al) particles or dendrites are discovered in the microstructure of the Al-20Si-2Cu-0.4Mg-1Ni alloy. Rapid cooling generated by squeeze casting process rather than the pressure is considered as the main reason for the formation of non-equilibrium α(Al) phase. The sound pressurizing effect of ultrasonic vibration also enables the non-equilibrium α(Al) phases to form above eutectic temperature and grow into non-dendritic spheroids in the process of semi-solid slurry preparation. Non-equilibrium α(Al) phases formed in the hypereutectic Al-Si alloy with ultrasonic vibration treatment, consist of round α(Al) grains formed above the eutectic temperature and a small amount of fine α(Al) dendrites formed under the eutectic temperature. The volume fraction of primary Si particles is decreased significantly by the effect of ultrasonic vibration through increasing the solid solubility of Si atoms in α(Al) matrix and decreasing the forming temperature range of primary Si particles. The average particle diameter and the volume fraction of primary Si particles in microstructure of the swash-plate by rheo-squeeze casting are 24.3 μm and 11.1%, respectively.