中英文翻译-铅元素对AZ91镁合金形成过程的影响.doc

Effect of Pb addition on ageing behavior of AZ91 magnesium alloy Abstract The ageing behavior of AZ91 alloy containing 2wt.% lead is investigated. The results show that addition of Pb suppresses the discontinuous precipitation and thereby slows down the ageing kinetics. Even though the peak hardness obtained for both alloys is almost same, the peak hardness reaches after 2400min for Pb added alloy against 900min for the base alloy. The presence of Pb in solid solution might have inhibited the diffusion of Al and Mg atoms, which is essential for the formation, and growth of discontinuous precipitation in this alloy. Keywords: AZ91 magnesium alloy, Pb addition, Ageing behavior, Microstructure, DTA 1. Introduction Magnesium-based alloys are increasingly used in the auto-mobile industries. The reasons for this lie principally in their improved speci?c properties compared with aluminum alloys or steels and light weight (30% less than Al, and 75% less than steels) [1]. Among the most common commercial magnesium alloys, AZ91 is endowed with one of the best combinations of castability, mechanical strength and ductility [2]. Presence of aluminum provides mechanical and casting properties as well as corrosion resistance, whereas zinc contributes to solid solution strengthening. The maximum solid solubility of alu-minum in Mg is 12.7wt.% at 437 ?C and decreasing to about 2wt.% at room temperature. Hence castings (sand and perma-nent mould castings) of this alloy are heat-treated to obtain better mechanical properties and studies are available in the lit-erature to understand the ageing behavior of this alloy [3–6].During solution treatment at 410℃, the Mg17Al12—βphase redissolves in to the Mg matrix and forms a homogenized solid solution. On subsequent ageing at lower temperature, aluminum precipitates out in two forms: i.e. discontinuous and contin-uous precipitates. Discontinuous precipitation is the cellular growth of alternating layers of phase (Mg17Al12) and near equilib