Study On Microstructure And Properties Of High Performance H.ypereutectic Al-Si-Cu-Mg Alloy

Hypereutectic Al-Si-Cu-Mg alloy with the quality of high specific strength,high hardness,low linear expansion coefficient,good wear resistanceand thermal stability,is an ideal piston materials for automotive engine.However,thelargeprimary Si and the coarseflakeeutectic Si could split the matrix in the conventional gravity casting of hypereutectic Al-Si-Cu-Mg alloy,which could effect of the alloy properties.Therefore,improving the morphologies of primary Si and eutectic Si to improve the alloy properties has become the focus of research on the application of hypereutectic Al-Si-Cu-Mg alloy at home and abroad.This test adopted thedifferent methods of modification,alloying,squeeze casting and heat treatmentto improve the microstructure and the mechanical properties of the alloy.The effects of modificationand alloyingon microstructure and mechanical properties ofthehypereutectic Al-Si-Cu-Mg a lloy were investigated.The results show that the coarseflakeeutectic Si in the alloy is changed into the tiny fibrous with the addition of the Sr.In the modification of the squeeze casting alloy,the fine block primary Si in the squeeze casting has grown up,andthe tensile strength and elongation of the alloy decreased obviously.It is mainly that the formation of Al-Sr-P has weakened the effect of modification.The Sr modification of squeeze casting alloy has the better comprehensive mechanical properties and the tensile strength of 203.67 MPa,the elongation of 2.95% and the brinell hardness of 113.13 HB.Alloying elements Ni,Cr and Mo can be added to improve the mechanical properties of the alloy,improved microstructure hypereutectic Al-Si-Cu-Mg alloy.The petal Al-Si-Mn-Fe multi-component phase in the alloy is changed intograiny phase and dispersed homogeneous distribution of reinforcements in the matrix,hindering the movement of dislocations and pinning the matrix.Themechanical propertiesof the alloying squeeze casting alloy isthat the tensile strength reaches 203.67 MPa,the elongation reaches2.95% and the brinell hardness reaches 113.13 HB.The squeeze casting alloys make three different pressing force of 398 MPa,598MPa,796 MPa.With the increase of pressure,the primary Si phase size has become smaller after disappearing;eutectic Si phase has also been significantly refined,evenly distributed,the number of α-Al dendrites in the alloyhas increased significantly,and has become more refinement and development.The alloy had the better comprehensive mechanical properties and the tensile strength reaches231.5MPa,the elongation reaches2.68% and the brinell hardness reaches124.10 HB at the pressure of 598 MPa.The effect of heat treatment on the microstructure and mechanical properties of Al-17.5Si multi-component alloy is investigated.While the solution treatment temperature and the solution treatment time are changed,the tip and the groove of the Si phase is dissolved and granulated gradually,and the massive primary Si phase has refined and spheroidized,and the edges and tip passivation of it gradually.The Si began to grow coarsening when the solution temperature is too high or the solution time is too long.In the same time,the precipitation of Al2 Cu,AlNi and multi-component phase of alloy also changed obviously,and the passivation phenomenon occurred in the heat treatment process.The friction and wear resistance of the squeeze casting Al-17.5Si multi-component alloyshas greatly influenced by heat treatment,which improved the wear resistance of the alloy.The alloy with the heat treatment 1h and 12 h have good mechanical properties,the tensile strength reaches 274.5MPa and 286.67 MPa,the hardness reaches 130.63 HB and 144.07 HB,the elongation is 4% and 4.32%,and the wear is similar.