Relationship Between Liquid Electrical Resistance Variation And Solidification Microstructure Of Sn-20%Pb Alloy Effected By Ultrasonic Treatment

A mass of researches indicate that ultrasonic pretreatment can significantly refine the solidification structure of the low melting point alloy, such as Mg, Al, and Sn-Pb alloys. The essence of ultrasound refining technique is the Nonlinear effect caused by sound cavitation and sound flow Metal alloy solidification behavior include two process of nucleation and growth. The influence of solidification behavior should be related to the microstructural changes. Resistance, a sensitive physical quantity to the micro structural, can reflect the structural changes. So we can understand the effects of ultrasound on the solidification behavior of the mechanism by observing the changes of resistance. In this article, as a part of National Science Foundation project "the relational research between ultrasound on solidification behavior of Mg alloy melt and melt resistivity changes", the resistance changes of Sn-20%Pb under ultrasound processing conditions were measured comprehensively and the corresponding solidifying structure was observed, influence of the system and the corresponding solidification organization, trying to build up to observe the ultrasonic melt resistance changes and solidified the correlation between the organization, and the refinement of mechanism of metal solidification organization after ultrasound trentment are revealed The main conclusions are as follows:(1) The melt resistance significantly reduced(AR) under Ultrasound treatment, remains small resistance drop(Ar) after ultrasonic stop and need time (Δt2) back to the original state before ltrasound treatment. Research shows that |ΔR| reflects the influence of the cavitation and sound flow effect to resistance under ultrasonic treatment,|Δr| reflects the melt micro structural change caused by ultrasonic cavitation effect,Δt2 reflects the valid time under ultrasound treatment;(2) Ultrasonic power and ultrasonic processing temperature influence significantly AR andΔr (?)f Sn-20%Pb alloy melt resistance. Improving ultrasound power or increasing processing temperature makes|ΔR| and |Δr increased; And the influence of processing time to |ΔR| is very small. Extending the processing time increased |Δr| a little that no longer changes after a period of time. (3) Through the comparison of the ultrasonic treated valid timeΔt2, improving ultrasound power or processing temperature and extending the ultrasound processing time, madeΔt2 of Sn-20% Pb alloy significantly extend, of which theΔt2 was up to 155 min at 330℃and ultrasound treated 5 min at 800 W;(4) The resistance measurements of different Sn-Pb alloy melt composition show that the increase of Sn content made |ΔR| and |Δr| increased significantly. In other words, under the ultrasonic treatment on high Sn alloy melt,ultrasonic cavitation occurred easily and the melt structure could be changed easily as well;(5) Continuous melt resistance measurement of Sn-20%Pb alloy at cooling process show that, The initial solidification temperature of alloy changed on the process of solidification,the initial solidification temperature went up and down with ultrasonic power increase;(6) The observation of relationship between organization and |Δr| in the heating process show that ultrasonic pretreatment could refine significantly coagulation organization of Sn-20% Pb alloy melt. In the heat preservation process |Δr| and solidified organization grain size had a function relation. The melt structure change caused by Ultrasound is the root cause of the refining solidification structure. Therefore, if the resistivity data accumulated fully, we can use |Δr| to forecast the melt solidification organization. This is very important to the ultrasonic pretreatment melt solidifying structure.