MICROSTRUCTURE EVOLUTION AND PROPERTY CHANGES OF Al-Si-Cu ALLOY BY CONTROLLING DIRECTIONAL SOLIDIFICATION PARAMETERS

摘要

As the properties of the Al-Si-Cu alloy depend on the microstructure, it is necessary to study the effects of processing parameters on the microstructure to control the properties of the Al-Si-Cu alloy. A novel Al-Si-Cu alloy rod was prepared using directional solidification (DS) of liquid metal cooling and the Al-Si-Cu alloy rod was investigated by using a scanning electron microscope (SEM), a JVJ-50s test machine, a MHVD-1000IS microhardness tester and a FT300 resistivity tester. The SEM was used to capture micrographs. The JVJ-50s test machine was employed to measure stress-strain relationships. The MHVD-1000IS microhardness tester was used to measure the microhardness of the specimens. The FT300 resistivity tester was used to evaluate the electrical conductivity. Experimental results indicate that the dendrite structure of the microstructure can be refined by increasing the melting temperatures during DS, but the exorbitant temperature would make the precipitated phase coarsen. It was found that when the melting temperature was 750 °C and the pulling rate was 300 μm-s~(-1) the maximum tension strength and microhardness were 232 MPa and 102 HV, respectively. Moreover, when the vacuum was 0.4 × 10~(-3) MPa, the electrical properties of the alloy are the best, i.e., the minimum resistivity was 17.6 μΩ-mm. Therefore, a set of optimum processing parameters, i.e., the melting temperature of 750 °C, the pulling rate of 300 urns' and the vacuum of 0.4 × 10~(-3) MPa, can be selected to improve the microstructure and properties of the Al-Si-Cu alloy.