Effect Of P On Microstructure And Properties Of Al-50% Si Alloy

Due to their excellent characteristics:low density,low thermal expansion coefficient,high thermal conductivity and good wear resistance;hypereutectic Al-Si alloys are widely used in aerospace,automotive and electronic packaging fields,etc.However,the coarse primary Si in the hypereutectic Al-Si alloy distributes randomly in the matrix,which severely separates the continuity of the aluminium matrix.And when subjected to the force,the tip of coarse primary Si is likely to cause local stress concentration,which significantly reduces the performance of the alloy.To increase the properties of the hypereutectic Al-Si alloy,it is necessary to refine the size and improve morphology of the primary Si in the alloy.This paper,studying on Al-50%Si alloy for electronic packaging materials,mainly studies the effect of different ingots thickness and P contents on the morphology and size of primary Si,and analyzes nucleation,growing process and modification mechanism of primary Si and investigates the influence of size and morphology of primary Si on the properties of the alloy.The following conclusions can be drawn:(1)The primary Si in the un-modificational Al-50%Si alloy mainly shows lath-shape with high aspect ratio.P can effectively reduce the size of primary Si and improve its morphology.As the P content increases in the alloy,the morphology of the primary Si changes from a lath-shape to an octahedral shape.The decreasing of ingot thickness is also helpful to reduce the size of primary Si,but has no effect on its morphology.(2)The AlP phase regards as the heterogeneous nucleation point of the primary Si.When the Cu-P modifier is 3%and the ingot thickness is 15mm,the primary Si in the Al-50%Si alloy is small,regular block.And its average size is minimum for 26.48?m.(3)Refining size of the primary Si and improving its morphology can effectively increase the hardness and wear resistance,and decrease CTE of Al-50%Si alloy.When the content of the Cu-P is 3%and the thickness of the ingot is 15mm,the hardness of the alloy reaches its maximum value of 198.1 HV,and the minimum values of average friction coefficient and wear depth were 0.407 and 12.59?m,respectively.(4)Adding P in Al-50%Si alloy can change the wear behavior of alloy.The wear mechanisms of un-modificational and owe-modificational alloys are mainly abrasive wear and delamination wear;when the Cu-P content is 3%,fatigue wear and abrasive wear play a dominant role in the alloy;the wear mechanisms in over-modificational Al-50%Si alloy are adhesive wear and abrasive wear.