Two-step Aging Treatment And Filling-solidification Process Simulation Of Aluminum Allog Pistons

The piston is the heart of the engine, it should have excellent mechanical properties, thermal stability and high wear resistance because of its working conditions. In order to improve the mechanical properties and microstructure of the piston, we used two-step aging treatment to instead of the traditional single aging treatment in this paper.The strengthening mechanism of the alloy after aging treatment were also discussed via SEM, TEM, XRD etc. In addition, we designed the permanent mold of a piston which will be produced by the factory and used UG software to make three-dimensional graphics. The parameters were modified and the casting flaws were be forcasted by the numerical simulation of the filling and solidification process using the MAGMASOFT.By changing the time and temperature of the two steps in the aging process,we can observe the change of mechanical properties and microstructure. The research has been found that:the primary Silicon’s size is smaller and its distribution is flareout after the aging treatment.The optimum two-step aging treatment process is:first aging at150for2.5h, and then aging at220for2.5h.The tensile strength is335MPa, the top of the piston’s hardness is75.0and the skirt section is74.8.Its metallographic structure meets the first-grade standard, and the volume stability is qualified.The strengthening mechanism of the alloy was analysed, the result is that: strengthening phases were precipitated during the aging process, which mainly contained:Mg2Si,S-A16CuMg4, Q-A18FeMg3Si6.The major factors for strengthening mechanism include:the precipitates were semi-coherent to the matrix; In the sliding process, the dislocation lines were tangled when they met the precipitates; The second phase was dispersed because of its growth process was very slow, effectively restrain local plane slip.Combined with traditional factory production experience and the characteristics of the piston, mould was designed. The parameters were modified and the casting flaws were be forcasted by the numerical simulation of the filling and solidification process using the MAGMAS OFT. The result forcasted that in the skirt and the top of the piston and the section between the top and hinge pin will prosbily have tarce amout of shrinkage cavity. And the higher the temperature is, the more the casting flaws are not obvious. In practice, we casted the pistons under the temperature of750℃, using the mold designed by ourself,and found that there are few shrinkage cavity.