Influence Of Heat Treatment On Microstructure And Properties Of Zn-Al Alloys

A series of experiments and tests have been done to systematically see theinfluence of heat treatment on microstructure and properties of highZinc-Aluminum alloys. By adjusting the heat treatment parameters, a best heattreatment process was obtained. Systemmatical research on the distribution ofcopper element has been done to get the regularities to guide other similar heattreatment of Zn-Al alloys.Relationship among different parts and their properties influenced by heattreatment process has been discussed. Main conclusions obtained are shown below:(1) The microstructure of Binary Zn-Al alloy consists of α matrix andα+ηeutectoid around α phase. Add of copper has no evidently change on thedendritic structure of Zn-Al alloys. Copper element solution in Zinc and Aluminumwhen the amount is low and precipitate together with Zinc to e phase when theamount is high. ε phase distributes in grain boundary area and grow with thecontent of copper.(2) The Brinell hardness of Zn-Al alloys grow with copper content (from0-5%).solution contributes more than precipitation in the growth of hardness. Wear lossdecreases with hardness and the coefficient of friction reach the lowest at coppercontent of2-3%.(3) Solution heat treatment makes the distribution of alloy elements ofZn-40Al-4Cu alloy homogeneous, turn the dendrites structure to small bulks. Theamount of α grows slightly with solution time while eutectoid decreases. ε phasebecomes round, the amount and size become small. The hardness and wearresistance of Zn-40Al-4Cu alloy improved evidently after solution heat treatment.Micro hardness of α phase increases with solution time while Brinell hardness andmicro hardness of eutectoid decreases.(4) Step solution heat treatment improves Brinell hardness of Zn-40Al-4Cualloy and micro hardness of α phase, improves wear resistance. The alloys treatedby the process of380℃×3h+400℃×1h+water quenching shows the best generalproperties. (5) Step solution heat treatment improves the homogenous of microcomposition of ZA40alloy, Brinell hardness and wear resistance and at the sametime reduces the coefficient of friction.(6) Wear loss of step solution heat treated ZA40alloy increases with appliedload, decreases with sliding speed; the coefficient of friction is lowest at mediumapplied load.