Research On Processing Of Centrifugal Casting Functionally Gradient Pistons Of Al-matrix In-situ Composite Reinforced By Mg₂Si∕Si

Hypereutectic Al-Si Alloy is an ideal material of pistons because it have low density and low expanding and higher wear resistance and dimensional stability.This paper focuses on technology of hypereutectic Si-Al-based in-situ composites reinforced by primary Si and Mg2Si for piston gradient preparation. We add elements enhanced such as Mg etc in hypereutectic Al-Si alloy composite material as the materials of the piston and designed a centrifugal casting mold and sand-cores and chosed reasonable process parameters, centrifugal casted several pistons.A material is be producted by adding Mg in hypereutectic Al-Si Alloy to form Mg2Si as reinforcement.We centrifugal cast pistons of A material of primary Si and Mg2Si particles gradient distribution at pouring temperature are 750℃and 780℃when the mold is preheated the temperature to 450℃. Adding Mg, Cu, Ti, Ni, Mn In hypereutectic Al-Si alloy to form Mg2Si, Al2Cu, Al2CuMg, W(A1XMg)5Si4Cu4 as reinforcement,we manufacture B material.We centrifugal casting pistons of B material of primary Si and Mg2Si particles gradient distribution at pouring temperature are 770℃and 820℃when the mold is preheated the temperature to 550℃. Each piston is taken sample to observe the distribution of the primary Si particles and Mg2Si.The gradient distribution of Mg2Si primary Si particles in the pistons at higher mold temperature and pouring temperature is more clear, indicating that mold temperature and pouring temperature is conducive to high particle segregation.All samples are made solid-solution and aging heating treatment .As testing the hard-ness and wear resistance in cast and heat-treatment state,we find that the hardness and wear resistance and the distribution of primary Si particles and Mg2Si have great relationship that the higher the density of particles the higher the hardness and the better wear resistance. Primary Si is the first factor of strengthening materials and Mg2Si are indispensable and the second factor of strengthening materials. B material is better than A at hardness and wear resistance that explain Mg and other elements strengthen the composite together than Mg alone well.By observing and analyzing microstructure of each sample in cast state and heat-treatment state we can conclude that primary Si has been refined at between 30-100um through the metamorphism. Mg2Si particles has also been refined at between 20-50um.Through the experimental research we manufacture the piston of gradient the distribution of primary Si particles and Mg2Si.There is very high density of particles at the top of the piston. cardiac acceleration of Mg2Si more than primary Si and Mg2Si promote the segregation of primary Si. This study has laid the foundation to the future research and provide important the basis of the technology...