Research On Friction And Wear Properties Of Particle Reinforced Graded Aluminum Matrix Composites

The preparation and wear behavior of SiC particle-reinforced aluminum matrix composite were researched in this paper stems from the project of 863 Project (Research on the preparation technology of aluminum matrix gradient composites and its application of the brake parts), which can supply a reference for the research and applications of particle reinforced aluminum matrix composites.Five kinds of graded composite materials (SiCp/Al-7Si, SiCp/Al-17Si, SiCp/Al-20Si, SiCp/Al-20Si3Cu and SiCp/Al-20Si4.5Cu) were produced by new spray deposition technique, which SiC particles continuous gradient between 0%~30%(wt%). Densification hot-pressing were adopted in order to improve various properties of the deposited billets. The friction and wear properties of deposited and hot-pressing billets with different silicon and copper content under different applied load and sliding speed were carried out on MG-2000 high temperature and speed friction wear testing machine at room temperature. On this basis, wear behavior of SiCp/Al-17Si and SiCp/Al-20Si3Cu gradient composite were studied at different temperature (50℃, 100℃, 150℃, 200℃), and the wear surface and sub-surface morphology of gradient composite were observed using scanning electron microscopy.The following conclusions can be drawn from experimental studies.(1) Obviously gradient distribution SiC particles can be obtained by using new spray deposition technology in gradient composite materials, and the hardness and wear resistance of billets increased after densification hot-pressing. The hardness of the composite improved significantly with the increasing of the content of SiC particles.(2) At room temperature, the friction coefficient of the gradient composite decreased with the increase of load and sliding speed, but the gradient change is not obvious. Hot-pressing material has a higher friction coefficient than deposited material, which caused by different bonding strength of SiC particles with matrix. The hardness and friction coefficient of the material increased with the addition of copper, which changed not obviously with different silicon content.(3) The load and speed have significant influence on the wear rate at room temperature, and there is a critical value from mild to severe wear transition. The wear rate decrease with increase the SiC content at different speed and load. The wear rate is minimal compared to other silicon content composites when silicon content is 17%. When the copper content is 3%, the graded composite material has best wear properties among different Cu content.(4) The effect of ambient temperature on wear resistance of the SiCp/Al-17Si and SiCp/Al-20Si3Cu was similar. The friction coefficient first decreases and then increases with the temperature increase from 50℃~200℃, and the critical temperature for both materials is 150℃. The effect of SiC content gradient on the friction coefficient is not significant. The wear rate for both materials is first increases then decreases and finally increases with temperature increase, which suddenly increases at the temperature 150℃and transits from mild wear to severe wear. The wear rate reduced significantly with the SiC content gradient increase.(5) The wear process of gradient composite can be divided into three stages under room temperature. Firstly, slight wears, which dominant mechanism is abrasion. Secondly, the formation of Mechanical Mixed Layer, which mechanism is adhesive wear together with slight oxidation wear, and the wear rate decreased in this stage ascribe to the protection of mixed layer. The last stage is the Mechanical Mixed Layer delaminated, which main mechanism is delamination wear,and the wear rate in this stage increase suddenly. Under high temperature conditions, the critical value for mild wear to severe wear transit was less than room temperature, but the wear mechanism was similar. Abrasive wear acts interaction with adhesive wear in the early stage, and oxidation wear acts together with delamination wear at later stage. The characteristics of mechanical mixed layer sub-surface for different materials are different after wear experiment. The thickness of sub-surface increase with temperature rises, and the extravasation element at sub-surface gradually decrease as the distance form the wear surface increasing.