| Hypereutectic silicon aluminum alloys are applied in the automotive and electronic packaging industry due to those outstanding performances. With the increase of silicon concentration, the wear resistance and heat stability of Al-Si series alloys improved, and the coefficient of expansion decreased. However, the flake and massive of silicon phase in the alloy seriously influenced the mechanical properties and limited the further development. In addition, there were inadequacies at the modification and powder metallurgy technology. Based on the investigation, the hypereutectic Al-Si alloy was fabricated with Spray Conform technique. The Al-20Si alloy rods of 8mm in diameter were fabricated under the condition of extrusion ratio of 7,10,13,17 and 21. The alloys microstructure was studied, and the mechanical and wear resistance properties of alloys at different extrusion ratio were tested. The results were as follows:（1） The components of atomized particles were difference due to the inhomogeneity of the melt, which could influence the distribution of primary silicon in the spray preform. However, the primary silicon was fragmented in the extrusion processing, and the fragments of primary silicon diffuse with the flow of matrix. The non-uniform phenomenon of spray preform could be eliminated.（2） The primary silicon particle was fragmented in the extrusion process. With the increase of extrusion ratio, the primary silicon became finer and more uniform. When the extrusion ratio was 21, the equal-area-circle diameter and variance were 3.3μm and 0.7, respectively.（3） The density, hardness and mechanical properties of as-prepared alloys were studied. The results indicated that Spray Conform method could effectively retard the nucleation and growth of primary silicon. With the increase of extrusion ratio, the relative density, hardness and tensile strength of Al-20Si alloy increased. When the extrusion ratio was 21, the density of Al-20Si alloy reached 99.7%, the hardness of Al-20Si was 91.8HRB and the tensile strength of Al-20Si alloy reached 210MPa. However, with the increase of extrusion ratio, the elongation of Al-20Si alloy first increased from 9.7% to 15.8%, and then declined from 15.8% to 9.2%. The fracture morphology of Al-20Si was investigated by scanning electron microscope, and the results showed that the fracture mechanics was ductile fracture.（4） The pin-on-disk friction wear testing machine and scanning electron microscope were used to study the wear resistance and the surface morphology, respectively. The results indicated that the wear resistance of Al-20Si increased with increase of extrusion ratio, and the wear rate were 5.×10-10g/（N·mm）,4.9×10-10g/ （N · mm）,4.5×10-10g/（N·mm）,4.2×10-10g/（N·mm） and 4.0×10-10g/（N· mm）, respectively. The average friction coefficient was decreased with the increase of extrusion ratio. In addition, the scanning electron microscope results indicated that the wear mechanisms were mainly abrasive wear, adhesive wear and fatigue wear.
|
PDF Full Text Request