Microstructure And Mechanical Properties Of ZA12 Alloy Prepared By Mixed Solid-liquid Casting

Zn-Al alloy shows considerable promise for bearing and wear applications, which is a new kind of antifriction material with high bearing capacity and mechanical properties, fine casting characteristic, low friction coefficient and low cost. There has been a growing interest and application in the use of such alloy.ZA12 alloy is the general-purpose alloy, and it has excellent machinability and high compactability. There is growing evidence that ZA-12 has excellent bearing and wear characteristics. The mixed solid-liquid casting is a new technology used for preparing microcrystal, which has been of real significance in applications of Zn-Al alloys. In this thesis, mixed solid-liquid casting was employed to prepare ZA12 alloy. The effects of processing parameters on the microstructures of mixed solid-liquid casting ZA12 alloy were mainly investigated and compared with ZA12 alloy prepared by other technologies. In addition, the evolution of ZA12 alloy microstructures has been obtained. The mechanical properties, friction and wear characteristic and mechanics of ZA12 alloy prepared by different technologies were also explored.The results are concluded as below:1)The processing parameters have important effect on the microstructures and mechanical properties of mixed solid-liquid casting ZA12 alloy. The result shows that homogeneous and finer nodular primary phases could be obtained with 40℃degree of melt superheat, 30% mass ratio of the added power and 38~74μm of powder particle size, at the same time, it has lower content of primary phase.2) Mixed solid-liquid casting ZA12 alloy has obviously cracked dendrites, homogeneous and fine nodular no-dendritic primary phases and reduced mean size compared with as-cast structure; and it is also much better than semi-solid structure which was agitated without powder added. The density of the ZA12 alloys prepared by mixed solid-liquid casting and semi-solid casting is lower than that prepared by metal mold casing.3)All of the alloys prepared the three technologies are composed byη-Zn phase,β-AlZn phase and a small quality ofα-Al phase.4)Because of impurity and gas cavity induced by smart agitating, the tensile strength has not been increased. The metal mold casting alloys exhibit mainly cleavage fracture, and the mixed solid-liquid casting and semi-solid casting consist of cleavage fracture and quasi-cleavage fracture. 5)The processing parameters of Mixed solid-liquid casting play an important part in Brinell hardness of ZA12 alloys.6)The testing load, rotational speed of friction ring and lubricating conditions have great influence on friction and wear characteristic of ZA12 alloys. At room-temperature, the mixed solid-liquid casting ZA12 alloy has the more excellent the friction and wear characteristic than metal mold casting and semi-solid casting alloys.