Microstructure And Mechanical Properties Of Squeeze Casting Hyper-eutectic Al-Si Alloy

The mechanical properties of Al-17.5 Si alloy can be significantly improved by squeeze casting.With the increase of squeeze casting pressure,the hardness,tensile strength and elongation of test alloys were increased significantly.When the squeeze casting pressure reached 600 MPa,the mechanical properties of test alloys obtain peak value.The morphology and distribution of phases of squeeze casting hypereutectic Al-Si alloy were significantly improved,the amount of bulky primary Si phase decreased,?-Al dendrite appeared and eutectic organization significantly refined.After Sr modification for Al-17.5Si alloy solidification under pressure,eutectic Si phases of test alloy were further refined,and then the mechanical properties of squeeze casting Al-17.5Si alloy increased.While P modification for Al-17.5Si alloy which solidified under pressure,amount of coarse primary Si particles increased remarkably in alloy,and then tensile strength and elongation of the alloy decreased.It can be conclude that Sr modification is suitable for squeeze casting hypereutectic Al-Si alloy.The microstructure of squeeze casting multicomponent hypereutectic Al-Si alloy were improved obviously.Beside appearing of ?-Al dendrite and the decrease in the number of primary Si,but also the size and number of those second phase?Al2Cu,Mg2 Si,Al7Cu4Ni and Al1.9Cu1.0Mg4.2Si3.3?decreased,and then the solid solubility of alloying elements in matrix increased.Squeeze casting improved mechanical properties of multicomponent hypereutectic Al-Si alloy.When the squeeze casting pressure were 600 MPa,hardness and strength of the alloy were reached peak.On the other hand,the microstructure and mechanical properties of squeeze casting Al-?15,17.5,22?Si alloy can be significantly improved,the wear-resisting performance of the alloy is effectively improve.Along with the increase of the content of Si alloy wear down further.Homogenization treatment of the squeeze casting Al-Si alloy improved mechanical properties and wear resistance.It can be mainly attributed to the improvement of Si phase morphology,size and distribution.During homogenization processing the morphology of Si phase experienced fusing and granulating process,Si phase is more rounded,distributed uniformly in matrix.After 525oC homogenization treated for 8¹2 hours,mean diameter of primary Si particles is about 2.0².5 ?m,comprehensive mechanical properties and wear resistance of test alloy reached best.After hot extrusion microstructure of squeeze casting hypereutectic Al-Si alloy changed significantly,developed ?-Al dendrite almost disappearance,coralloid eutectic Si phase were broken as small granular,average size about 2⁴?m,these fine Si particles are diffusion in matrix of alloy.in microstructure of squeeze casting hypereutectic Al-Si alloys the small hard Si particle uniform distributed in soft Al matrix,and then the potential of the alloy have been played.Hot extrusion forming for squeeze casting Al-17.5Si alloy billet can greatly improve the mechanical properties of alloy.Stimulation experiment of the squeeze casting Al-Si alloy was carried out for investigation of the best deformation condition of alloy.The result show that the stress level of squeeze casting alloy is higher than gravity casting,the deformation of squeeze casting alloy is harder,and the Q is 308.77kJ/mol.The optimum processing parameters were determined on the basis of processing map,deformation temperature is 450⁵00oC and strain rate is0.01⁰.1s^-1.Compared with gravity casting the tensile strength of squeeze casting Al-Si alloy raised 135% as well as the elongation raised 923.5% under the parameter obtained from the hot stimulation.