Heating Mode Az31 Magnesium Alloy Directional Solidification Organization Impact Study

Magnesium alloy is the lightest metal structural material, and viewed “themost promising green engineering material in the21stcentury” because of itshigh specific strength, high specific stiffness, dimensional stability,easy-to-hot-deformation, strong electronic and thermal conductivity, gooddamping capacity, electromagnetic shielding and easy-recycling.The study and application of magnesium alloy have drawn much attentionand some of them had been put into practices in various areas. Till now, thecombination of magnesium and directional solidification is rarely reported, so itis significant to study this technology.Some relevant achievement have be gained by Mr Chen and Mr Zhao, whomade some investigation on AZ31and AZ91respectively. This paper is, on thebasis of existing results, to optimize the procedure and microstructure of AZ31by adjusting heating methods and other factors.Two heating methods of Si-C resistance furnace and intermediatefrequency furnace (two and nine turns induction coils) are adopted to solidifyAZ31magnesium alloys respectively. Different solidified samples are preparedat various stretching speed and temperatures and the effect of heating methods,temperature and stretching speed on the microstructure is systematically studiedby the metallurgical organization and curves of time and temperature. Thefollowing is the results achieved.（1）Compared to Si-C resistance furnace, intermediate frequency furnacemakes lower-position peak-temperature point and more narrow melting area,which makes maximum temperature closer to solidification surface, and thenenlarge the thermal gradient and benefits the growth of column crystal. Inconclusion, intermediate frequency furnace is superior to Si-C resistancefurnace in term of preparing directional solidified column crystal.（2）Using medium frequency induction heating, ideal columnar structurecan be achieved at temperature873℃,at the drawing speed of8μm／s. Whenthe drawing speed is lowed, the grain size became bigger for fuller growing.(3) Medium frequency furnace of two turns is used to prepared directional solidified column crystal of AZ31. the second phrase (βphrase) in the preparedsample shows different characteristic from traditional cast sample, includingclear boundary and a small amount of round second phrase spreading at grainboundary.(4) Medium frequency furnace of nine turns is then employed in theexperimental, in which temperature is1100℃, stretching speed is25μm/s. thesecond phrase of AZ31is tadpole-shaped and black at the early stage of graingrowth, and become ball-shaped with the process of experimental and disappearat the last.