Influence Of PTFE On The Microstructure And Properties Of Al-Ni Composites Fabricated By Friction Stir Processing

A series of Al-Ni composites were fabricated by friction stir processing,and then were post-treared at different temperatures.The effect of the different amounts of PTFE and heat treatment on the microstructure and properties of Al-Ni composites fabricated by friction stir processing were studied.The reinforced powder and distribution of Al-Ni composites were studied by SEM、XRD and EPMA.The strengthening mechanism of PTFE on Al-Ni composites fabricated by friction stir processing were studied.The results show that the uniformity of the Al-Ni composite has been improved significantly by adding PTFE;Within a certain range,the uniformity of composites raised with the increase of the amount of PTFE.When PTFE content recched 7%,The tensile strength of composites can reach 233 MPa,compared with the pure Ni(The tensile strength is 163MPa),the tensile strength of composites has increased by 43%,and composites strengthening effect is most conspicuous;When PTFE content exceeded 7%,the tensile strength of composites was decreased somewhat,but the tensile strength keeps higher than pure Ni.The pure Ni and 7%PTFE mixed powder Al-Ni composites were treated at 450,500 and 550℃ for 6h.Results show that the Al-Ni composites prepared are composed of Al3 Ni,and a few Ni is not participated into reaction.Within a certain range,the Al-Ni reaction increased with the rise of the temperature,and more intermetallic compounds appear,the component mainly is Al3 Ni and Al3Ni2.the tensile strength and elongation of Al-Ni composites were 142.5MPa and 12% respectively after heat treatment.Compared with the pure Ni composites,the tensile strength of composites has reduced.The tensile strength and elongation of 7%PTFE mixed powder Al-Ni composites was decreased somewhat after heat treatment.Among them,The tensile strength of 7%PTFE mixed powder Al-Ni composites was 173 MPa,Compared with the 7%PTFE mixed powder Al-Ni composites,The tensile strength are reduced by 25.8%.The reinforced powder and distribution of different stages were studied during the composites were fabricated by friction stir processing when was divided into five stages.For the first stage,the PTFE as the lubricating mediums showed distinct lubricating effect on the Ni.Under the action of tool,the unreacted Ni showed onion rings distribution in the Al substrate.For the second stage,the temperature of complex zone during the composites were fabricated by friction stir processing higher than the melting point of PTFE,the lubricating effect of PTFE can not react with Ni,so the agglomeration of little Ni appear.Last,lots of heat were storaged in complex zone because of the repeatedly stir friction.The flowability of plastic metal on machining region become more excellent,the reinforced particle in Al-Ni composites distributes more uniform under the action of tool.