Research On Microstructure And Mechanical Properties Of Friction Stir Processed In-situ Aluminum Matrix Composites

Friction stir processing?FSP?,a new type of plastic processing technology,is developed based on the friction stir welding?FSW?.It has been widely used in the preparation of fine crystal structure and composite materials,the modification of heterogeneous material microstructure and in-situ reaction synthesis,etc.Selecting Al-Fe and Al-Fe₂O₃ system as the research object,this paper explores the atomic diffusion rule on hot force coupling condition by preparing in-situ composites by means of vacuum hot pressing and FSP.It also explores the influence of technical parameters on microstructure and properties of in-situ composites.Al-Fe₂O₃ composites were prepared by powder metallurgy,forging and FSP methods,and the mass fraction of Fe₂O₃ was 5%,10%and 20%,respectively.The Al-5Fe composites were prepared by the same method as Al-Fe₂O₃ composites.Observing microstructure by characterization methods such as XRD,optical microscope,scanning electron microscope,transmission electron microscopy?TEM?.X-ray diffraction?XRD?results showed that the intermetallic compound Al₁₃Fe₄ was generated in Al-20Fe₂O₃composites on forged state,but this compound did not appear in other composites on forged state.By adjusting the FSP processing pass,rotation rate and traveling speed,we can obtain in-situ composites of different reaction degree.it turned out that the metal atoms of Al-5Fe was activated,and generated Al₁₃Fe₄ by reaction after multi-pass FSP.Single pass FSP with low rotation rate can help generating Al₁₃Fe₄ in Al-5Fe₂O₃,Al-10Fe₂O₃ composites,Al-20Fe₂O₃ composites on forged state contained a certain amount of Al₁₃Fe₄ phase,and this phase increased when the heat input increased during FSP.FSP can effectively activate the in-situ reaction between Al-Fe and Al-Fe₂O₃ composites,and promote the formation of intermetallic compounds.By contrasting,we found Al migration caused by FSP obviously higher than that of annealing.Calculation shows that Al atom diffusion rate in the FSP is 10⁴ times the diffusion rate in annealing process.FSP,therefore,can quickly activate in-situ reaction.FSP can obviously enhance the mechanical properties of Al-Fe and Al-Fe₂O₃composites.The maximum tensile strength of Al-10Fe₂O₃ composites on forged state at room temperature is 124 MPa,and after 3 passes FSP,the tensile strength increases to 298 MPa.Maximum tensile strength of Al-10Fe₂O₃ composites on forged state in the 300oC environment is 65 MPa,and after 3 passes of FSP,the tensile strength of the sample increases to 96 MPa,which is much higher than pure Al?18MPa?.