Friction And Wear Performance Of Wrought Al-15Si Alloy

Hypereutectic Al-Si alloy has high electrical conductivity,low expansion coefficient,high wear resistance,good volume stability and low cost.As safety sliding contactor,hypereutectic Al-Si alloys have better wear resistance,electrical conductivity,and are cheaper than copper,aluminum,steel-aluminum composited material.In this paper,billet of DC cast phosphorous modified Al-15Si alloy with fine primary silicon particles and uniform casting structure was achieved.Hot extrusion was performed to produce profiles which were subsequently subjected to heat treated at 550? for 3h,5h,10h and 15h respectively.The micro structures and conductivity of the alloy in different processing stage were observed and analyzed by metallographic microscope,scanning electron microscope(SEM)and conductivity tester.The friction and wear behavior of as extruded alloy and heat treated alloy for 3h,15h were tested.Wear surface and sub-surface were characterized by SEM aiming at understanding the wear and friction mechanisms.The main conclusions are drawn as follows:1.The micro structure of the Al-15Si alloy achieved by the DC casting consists of the polygonal primary Si particles,the ?-Al dendrites,and the(?-Al+Si)eutectics.After hot extrusion,the needle and fibrous eutectic silicon in the as-cast structure evolve to fine particles which are uniform distributed in Al matrix along the extrusion direction.After 550? heat treatment,primary silicon particle become obtuse.The size of primary silicon ranges 25?m-26?m.Mean diameter of Si particles is 2.83?m after extrusion,and average diameter of Si particles are 4.25?m,4.40?m,4.72?m,4.75?m after heat treatment for 3 h,5 h,10 h,15 h respectively.The electrical conductivity of as-cast sample reach the minimum by 31.5%IACS and extrusion sample has a better conductivity which is 44.2%IACS.2.The friction coefficient and mass loss of Al-15Si alloy(as-extruded,heat treatment for 3 h and 15h)decrease as sliding distance increase.When the sliding distance reached 2000 meters,the friction coefficient change to 0.5651,0.5420,0.5244 respectively;mass loss are 46.6mg,39.4mg and 27.8mg.The best friction and wear properties can be obtained after heat treatment for 15h.3.The number of Si particles per unit area in as-extruded alloy is 689,which is larger than heat treatment for 3 h(257)and 15 h(241).The length-width ratio of silicon particles reduced from 1.96 to 1.55 and 1.50,and the roundness of Si particles increase bonding strength between Si particles and Al matrix which enhance the wear resistance.4.The wear mechanism of hypereutectic Al-15Si alloy is the abrasive wear and the micro-breakout wear.At the beginning of wear process,the surface of sample keeps abrasive wear and the sliding furrows parallel to the direction.The furrow of sample in heat treatment stage is deeper than that of as-extruded.The surface of sample generate plastic shear lips for plastic deformation,which produced cracks,fracture and brittle fracture after continuous rolling mill of the friction pair of metals.5.There are fractures inside of silicon phase particles in sub-surface or in the joint area between silicon particle and aluminum matrix.With the increase of wear time,the crack in sub-surface gather and extend to the surface,and then generating different size of spalling pit.