Conform Continuous Extrusion And Heat Treatment Of Al-13Si-xCu-yMg Alloy

The present research involved in a high alloyed Al-13Si-xCu-vMg (x+y=8～9, x>y) alloy. Conform continuous extrusion (CCE) was adopted to achieve uniform microstructure by severe plastic deformation. With subsequent solid solution and ageing treatment, the strength and wear resistance of the alloy were enhanced. Well comprehensive properties make it service better in many occasions including engine piston and rotor of air compressors. By investigation of homogenization, CCE process, solid solution and ageing of Al-13Si-xCu-yMg alloy, several conclusions are obtained as follow.By homogenization (465℃,12h, air-cooling), hardness of the alloy increases from78.7HBS to115.8HBS, non-equilibrium microstructure is almost eliminated, the spheroidization of eutectic Si initiate completely and the particles locate mostly at triangle grain boundaries. Big bulk of0phase re-precipitate at grain boundary at480℃. Overheat phenomenon is observed at510℃. Moreover, when the holding time extend to15h, fine0phase, Q phase and elemental Si precipitate attaching to the surface of eutectic Si, and continue to grow.Optimal parameters of a flat bar (18×4mm) by CCE process are obtained as extrusion speed of4.5rpm, exit temperature of447℃, extrusion rate of8.55. By process with parameters above, the as-cast alloy with high alloy element contents achieves severe plastic deformation. Finer microstructure and more obvious flow lines are contained in products manufactured by CCE. The hardness, strength σb and elongation δ of the as-extruded flat bar by CCE reach15.8HBS,112.6MPa and11.3%, which increase by23.7%,16.3%and48.7%, respectively, compared with the samples prepared by conventional extrusion.By solid solution (495℃,90min, water quenching) and aging (170℃,4h, air-cooling) treatment, the σb and hardness of the flat bar by CCE reach486.8MPa and152.0HBS, which improve by3.3times and31.3%, respectively, compared with as-extruded state. The ageing strengthening is mainly attribute to dispersoid distribution precipitation along (100)Al of fine plate-shaped θ’ phase and lath-shaped Q’ phase. The wear rate of as-aged sample is7.4667g/10-9.N-1.m-1, which is lower than as-extruded state by1.0666g/10-9.N-1.m-1. Adhesive wear and fatigue wear are determined to be the main wear mechanism of as-aged state, which is different from adhesive wear and abrasive wear of as-extruded state.