Effects of Magnesium on the Microstructure, Hardness, and Tensile Properties of Zinc Alloys Containing 25 to 40 percent Aluminum.
The Bureau of Mines evaluated the properties of zinc alloys containing 25 to 40 weight-percent al and 0 to 0.7 percent mg. Microstructures, hardness, and tensile properties were evaluated for material as extruded at 285 deg c, solution treated at 300 deg to 400 deg c, and subsequently aged at 100 deg to 200 deg c. The alloys without magnesium are characterized by low hardness and strength with high tensile elongation and reduction in area. It was verified that magnesium effectively retards the zn-al eutectoid transformation below 275 deg c and markedly increases hardness and strength with decreases in ductility. Solution treating at 350 deg c results in large grain sizes and gross embrittlement. Subsequent aging of the zn-al-mg alloys at 200 deg c restores ductility substantially and stabilizes the structures, but strengths are considerably reduced. Combined strength and ductility properties are better for the as-extruded condition than for any heat-treated condition. There is usually little advantage in overall tensile properties from increasing magnesium above 0.1 percent.