磁场作用下铝合金凝固过程的电阻变化

Variety of resistance of Al alloy under magnetic fields during solidification processing

为了确定磁场对铝合金凝固过程的影响,利用双电桥测试了Al-21%Cu、Al-22Si合金分别在无磁场、直流磁场和交流磁场作用下从液态到固态的电阻变化.分析了Al-Cu合金与Al-Si合金电阻-温度曲线的差别,研究了磁场对合金凝固过程中液、固相线温度及微观结构的影响.结果表明,Al-21%Cu合金的电阻-温度曲线呈单调下降趋势,且有两个明显的转折点,而Al-22%Si合金的电阻-温度曲线不再是单调下降,两个转折点也很不明显,在直流磁场作用下,Al-21%Cu、Al-22%Si合金的液相线、固相线温度均有所降低,在交流磁场作用下,两种铝合金的液、固相线温度均有所升高.在Al-Si合金凝固过程中施加外磁场时,抑制了初生β-Si的生成.

In order to valuate the effect of magnetic fields on solidification processing of A1 alloys, the variety of resistance of A1 - 21% Cu and A1 - 22% Si alloys changing from liquid to solid under no magnetic field, DC magnetic field or AC magnetic field was measured by double bridges four-terminal method. The differences of resistance versus temperature curves （ R - θ curves） between A1 -21% Cu and A1 -22% Si alloys were ana- lyzed. The effects of magnetic fields on the liquidus, solidus and microstructures of A1 alloys during solidification processing were studied through the analysis of R-θ curves. Results show that the R - θ curves of A1 - 21% Cu alloy monotonously decrease and have two obvious turning points, whereas the R - θ curves of A1-22% Si alloy do not monotonously decrease and the two turning points are not obvious at all. Under DC magnetic field the liquidus and solidus temperatures of A1 - 21% Cu and A1 - 22% Si alloys both decrease, while under AC magnetic field the liquidus and solidus temperatures both increase. Applying magnetic fields in sohdification of A1-Si alloy can restrain the producing of primary β- Si.