| Abstract:Hypereutectic aluminum-silicon alloy is an important casting alloys, and it have superiority properties like low density, high strength, high wear resistance and low thermal-expansion coefficient and so on.It be widely used in aerospace engineering and automotive manufacture. However, during the casting, the brittle primary silicon particles grow up quickly. It break the continuity of the aluminum body seriously and reducing the mechanical properties, which limit the further application. In order to change this situation, we improved the preparation process:using atomization hot pressing、hot extrusion process to get Al-23Si alloy, and we do some basic research about the microstructure and mechanical properties during every procedure of Al-23Si alloy.The raw material alloy powder Al-23Si-1Mg-2.9Cu-1.9Fe faricated by nitrogen atomization technology, we divided them in three parts according to the different grain size. This paper studies the phase structure, microstructure, thermostability of the raw powder; Preared the prepormed material using hot pressing technology. And the pressing temperature,powder size were optimized; The hot extruded alloy bars were prepared by above mentioned prepormed material. The extrusion temperature, extrusion ratio, the way of extrusion were discussed; The treatment process were optimized and the fracture mechanism、strengthen mechanism were studied as well.The results show that the particle size of1#、2#、3#atomized alloy powder were most focus in30μm～80μm,10μm～30μm,60μm～100μm separately。The phases of powder are mainly α-Al and irregular blocky primary silicon. The size of primary silicon focus in3～5μm. The results show that there are many tiny holes inside. In the atmospheric environment, as the temperature rises to500℃, the primary silicon grow up obviously. In the subsequent trials we should avoid the oxygen atmosphere.The microstructure and mechanical properties of vacuum hot pressing material showed that under the same pressure (lOMPa) condition the optimum pressing temperature is575℃. The material density reaches98%of the theoretical density, the tensile strength of1#(30-80μm)、3#(50-100μm) hot pressing material is230MPa.The results of hot extruded alloy bars show that the optimal extrusion conditions are:discontinuous extrusion, the hot pressing material heat preservation temperature is480℃、the extrusion pressure is330Mpa. After extrusion the alloy density close to theoretical density,0%porosity.We observed and discussed the microstruture during the extrusion process stages and different regions.The results of temperature orthogonal experiment show that the heat treatment condition:solution treatment480℃x8h, aging treatment180℃x8h. The results of microstructure and mechanical properties show that the size of primary silicon is less than10μm. In normal temperature condition, the tensile strength and hardness of1#(30-80μm)、2#(0-30μm)、3#(50-100μm) alloy were very close. The tensile strength is about440MPa,hardness is90HRB.The fracture is dominated by the cracking of brittle silicon phase and the peeling of silicon phase from matrix. It appears as brittle fracture in macro and there are dimple can be observed in microscope.And the tensile strength of2#(0-30μ m)、3#(50-100μm) alloy at300℃test condition are about200MPa. The thermal expansion during the range20℃～300℃is18.4423x10-6.This paper mainly focuses on how experiment process effect on microstructure and mechanical properties, and optimize the process. It has a reference value to study of hypereutectic Al-Si alloy with powder metallurgy technology. |
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