Research On Hot Drawing Of AZ31 Mg Alloy Wire

Magnesium alloy has low density, high strength and good biocompatibility which makes it have extensive application in the communications, aerospace and medical industry. Drawing forming is suitable to processing magnesium wire. But the plastic forming ability of magnesium is low at room temperature and drawing forming is very likely to produce cracks without frequent annealing treatment in the process of drawing, so the production efficiency is low. In this paper, cooling heat drawing process was proposed and severe plastic deformation(plastic deformation is30% per pass and cumulative deformation reaches more than 60% between annealing) had been obtained with infrequent annealing and higher efficiency.,which has great significance in research and application.Effect of drawing parameters( drawing temperature, pass deformation amount and cooling method) on AZ31 magnesium wire were discussed. Based on a comparison between continuous drawing methods with different times of annealing,the optimum one was suggested. In single pass hot drawing, there were more recrystallized grains when pass deformation amount was more severe. Even if the deformation is 30%, recrystallized grains were fewer than parallel shear bands and twinning which accounted for more than half of the whole. Texture type changes from original direction that(0001)< 0211 > is parallel to drawing direction to a new direction that(0001)< 0110 > is parallel to drawing direction and texture density increases with pass deformation amount increasing. Comprehensive mechanic properties of AZ31 magnesium wire are good when pass deformation amount is between 20%-25%.Drawing temperature and cooling conditions have significant influence on microstructure of magnesium wires. The percentage of recrystallized grains increased with drawing temperature increasing but most of the microstructure are shear bands and twinning, since there is not enough time for recrystallization when the wire is cooled by water. In contrast, the majority of microstructure is recrystallized grains if the wire is cooled in air. As a result, the permitted drawing stress of wires cooled in water is higher. When AZ31 magnesium wire is drawn under recrystallization temperature and cooled by water,(0001)< 0110 > or(0001)< 0211 > is parallel to drawing direction. Texture type changes to a single direction that(0001)< 0110 > is parallel to drawing direction and texture density, as well as strength of deformed wire, decreases with temperature increasing. In addition, strength of deformed wires is generally higher when they are cooled in water than in air.Two kinds of multipass continuous drawing process are made according to the research on drawing parameters through single pass hot drawing. The original AZ31 magnesium wire is drawn from Φ9.0mm to Φ1.9mm. The drawing temperature is400-210℃, and single pass deformation amount is above 20%. Everage cumulative deformation between annealing is 40.4% and 57.3% respectively. Comprehensive mechanical properties of wires drawn by the three pass per annealing continuous drawing process are best of all. Yield strength of deformed wires increases from the original 157.3MPa to 306.5-382.8MPa and tensile strength from 255.2MPa to349.8-417.1MPa. Besides, times of process annealing have decreased. So the proposed drawing process can be applied to AZ31 magnesium wire with small diameter.