Study Of The Microstructures And Mechanical Properties Of 4032 Alloy

The microstructures and phases of as-cast and as-distortion 4032 alloy were investigated by means of optical microscope(OM), scanning electron microscope(SEM) and X-ray diffraction(XRD), and the mechanical properties were measured by Brinell hardness tester and tensile testing machine.The formations of dendriteα-Al and cluster Al-Si eutectic structure were inhibited in the semi-continuous casting 4032 alloy on the chilling condition. On the condition of a certain extent cooling rate, the second dendrite arm spacing ofα-Al in the 4032 alloy ingot has a power function relation with the local solidification time and the relative exponent and coefficient were confirmed as 0.28094 and 9.253. Further, the relationship between the second dendrite arm spacing and the hardness has been confirmed minus exponential function.Combined with the simulation of stress and strain during the deformation with the Deform software, the microstructure analysis of 4032 alloy sample obtained by counter extrusion shows that the high strain is in favor of the microstructure homogenization and the mixture of soft matrix and hard second phase. The high stress has an obvious contribution to the fragmentation of hard phases which located among other hard phases, however, this contribution is limited when the hard phases contacted with the soft matrix.The texture analysis shows that the 4032 alloy bar has a strong <111> texture and a relatively weak <100> texture. The <111> texture appears only at the position of half radius of the alloy bar where the strain and stress is lower. However, at the edge where the strain and stress is higher the texture is replaced by the <211> texture which originates from the rotation of <111> extrusion direction by 19.5°. At the center of the extruded bar the {011}<655> texture appears to be stronger than {011}<111>.During hot extrusion process, the dynamic recovery occurres, leading to different soften degrees at different places of the alloy bar. The hardness decreases to 55HB, half compared to the as-cast alloy. As for the co-effect of the grain size and texture, the tensile strength exhibits no obvious differences at different distance to the center of the bar, which range around 180MPa~190MPa. In contrary, the elongation is up to 15.46% at the edge of the bar, whereas the elongation is only 7.87% at the center, which has a big difference according to the distance to the center of the bar. During the tensile deformation, compared to the fine silicon particle, the coarse nickel and ferrum rich phases are more easy to fracture, due to their brittleness nature.The mechanical properties of heat treated products show that the tensile strengths are higher than 360MPa, and the elongations range around 4%~6.8%. according to the microstructures of the heat treated products , the coarse nickel and ferrum rich phases have not been eliminated in the heat treatment but the homogenized microstructure has been obtained and the size of the hard phases have been controlled by the application of sever plastic deformation which is helpful to enhance the tensile property.