Zhang Jianfeng

EFFECT OF AC MAGNETIC FIELD ON ELECTRIC RESISTANCE OF Sn-20%Pb ALLOY

The electric resistance of Sn-20%Pb alloy was measured at different temperatures when the AC magnetic field was applied. The results showed that the AC magnetic field had no effect on the electric resistance of solid Sn-20%Pb alloy, but when it was applied on the liquid Sn-20%Pb alloy, the electric resistance of alloy increased gradually. After the AC magnetic field was stopped, the electric resistance remained at a constant value for a long time, and then slowly decreased to the value before applying the AC magnetic field. The results of metallographic microscope and SEM showed that the AC magnetic field not only refined the primary β-Sn grain, but also increased the Pb content in primary β-Sn grain, so that the distribution of Pb was more uniform than that in the sample without magnetic field. The Andersons theory of disorder has been used to explain the experimental results. It was considered that the electromagnetic stirring caused by AC magnetic field destroyed the short range order of the Sn-20%Pb melt, improved the disorder degree of the system, transformed some extended states electrons into localized states electrons, consequently increased the electric resistance of the melts.

CHANGE OF THERMOELECTRIC POWER OF LIQUID Al ALLOYS CAUSED BY DC MAGNETIC FIELD

The effect of DC magnetic field on the thermoelectric power of Al alloys at different temperatures was investigated in this work. The results showed that if the magnetic field intensity difference between the two ends of the sample was large, it would lead to a decrease in thermoelectric power of liquid Al-2.89%Fe Al alloys. When the magnetic field was removed, it took a period of time for the thermoelectric power to increase gradually to the initial value. This phenomenon had been observed in other Al alloys melt at different temperature. The higher the square difference of magnetic induction was, the more significant thermoelectric power changed. The approximate homogeneous magnetic field had no effect on the thermoelectric power. According to the theory of weak localization, the magnetic field can change the distribution of extended states electrons which contributes to the change of thermoelectric power.

超声处理对液态Pb-20%Sn合金电阻的影响

研究了不同处理温度（300,400和450℃）、不同超声功率（400,600和800W）以及不同处理时间（3,5,7和10min）对Pb-20%Sn合金电阻的影响.结果表明,超声处理对Pb-20%Sn合金熔体的电阻有显著的影响.超声作用使熔体电阻瞬间减小,停止超声作用后,电阻瞬间增大,但并未恢复到初始值,与初始电阻相比有一个减小量,该电阻维持一段时间后才缓慢恢复到初始值.超声功率越大,超声作用效果越显著,电阻瞬态变化量和持久性变化量越大,有效时间也越长.随着温度升高,电阻瞬态变化量和持久性变化量均增大,超声作用有效时间先增大后减小.随着超声作用时间的延长,超声作用效果逐渐增大,但存在一个饱和作用时间.