The Research Of Siliconized Microstructre And Friction & Wear On Aluminum-bronze With Packing Si

Compared with simple aluminum-bronze,complex aluminum-bronze has better wear resistance.It is mostly used to make frictional parts in mechanical transmission system,such as screw and nut.Complex aluminum-bronze is easy to wear out in the application as a friction pair with harder parts,which affects the service life of the parts.In order to enhance the wear resistance of aluminum-bronze without changing the mechanical properties of the matrix,the aluminum-bronze alloy was siliconized by pack cementation in this paper.The hardness of the alloy surface was improved by a certain thickness of siliconized layer,which includes diffusion layer and solid solution layer.The influences of different processes on the siliconized layer and the matrix were investigated by changing the ratio of siliconizing powder,heating temperature and holding time.The microstructure and the phase composition of the siliconized layer were tested and analyzed.The wear resistance of the siliconized layer was investigated with four factors:friction coefficient,wear loss,morphology of friction scratch and composition of wear dust.The results were as follows:(1)When the Si content in the proportion of siliconizing powder was 10%,30%,50%and 70%,the siliconized layer was about 100?m,200?m,140?m,130?m,respectively.The least number of holes were in the siliconized layer of 30%Si content.There were two kinds of hard and massive microstructures in the diffusion layer,the dark one was a fe-rich phase composed of intermetallic compound Fe Si and the light one contained the intermetallic compound Cu_0.83Si_0.17and Ni₂Si.Fe Si phase is harder than Cu_0.83Si_0.17and Ni₂Si.In the solid solution layer,the small or granular?phase was around the?phase.Fe,Ni and Si were relatively enriched in the siliconized layer,while Al mainly existed in the matrix.(2)The siliconized layer was 50?m,70?m and 100?m respectively when the heating temperature was 650?,750?and 850?.With the increase of temperature,the size of the holes in the siliconized layer and the?_IIphase in the matrix increased,the number of holes decreased,and the holes gradually concentrated on the alloy surface.However,there was no change in the microstructures of matrix at 650?and 750?.(3)When the holding time was 4h,6h,12h and 18h,the siliconized layer was 95?m,120?m,140?m and 170?m respectively.With the increase of holding time,the number of holes decreased but the size increased,the reticular?₂phase around the?phase and the size of?_IIphase in the matrix increased.When the holding time is 18h,the number of holes was the least but the size was the largest,and the number of massive microstructures was the largest.Distinct massive microstructures existed in all different holding time tests.(4)The average friction coefficient of the siliconized sample was about 1/2 of that of the original sample,and the amplitude of the friction coefficient was small.The lube in the original sample failed first compare to that in the siliconized sample in the same time.Large wear dust adhered to the surface was a large block,friction scratches were wide,the edge of a notch was rough,but siliconized sample was the opposite.The composition of the wear dust contained oxides from the surface of steel,which indicates that there are various forms of wear.The wear loss rate of the original sample was 3 times than that of the siliconized sample.In conclusion,when the proportion of siliconizing powder is 30%Si+3%Na F+3%NH₄Cl+64%Si C,the heating temperature is between 750??850?,and the holding time is between 12h?18h,a certain thickness of high quality siliconized layer will be obtained and the matrix won't be affected.The wear resistance of aluminum bronze can be improved by the siliconized layer and the service life of the parts can be extended.