| Improving the strength and wear resistance of aluminum alloy,the traditional ceramic particles reinforced aluminum matrix composites can reduce the plasticity and toughness,while the hard metal particles as the reinforcing phase can improve both the strength and plasticity at the same time.Due to its unique structure,high-entropy alloy(HEA)has excellent performance.Therefore,HEA is an ideal reinforcing material in terms of improving the strength and wear resistance of composites as well as material plasticity.In this research,Al Co Cr Fe Ni/5083Al composites were prepared with Al Co Cr Fe Ni HEA particles as the reinforcing phase,and the rapid cooling solid phase processing technology was used to avoid the interfacial intermetallic compounds caused by high processing temperature,considering the strength and plasticity of the composite at the same time.The preparation of the composites has practical significance for the application of aluminum alloy.The Al Co Cr Fe Ni/5083Al composites were fabricated by the underwater friction stir processing(FSP).The optical microscope,scanning electron microscope,X-ray diffractometer,microhardness tester,and friction and wear test equipment were used.The effects of using different number of passes(1,3,5-pass)FSP and the HEA particulate content(5,10,15 vol.%)on the microstructural uniformity,mechanical properties and friction and wear properties of Al Co Cr Fe Ni/5083Al composites were investigated,finally revealing the fracture,strengthening and wear mechanism of composites.The optimal processing parameters in this experiment were:the tool rotational speed of 1400 rad/min,travel speed of 40 mm/min,and the pressing depth of 0.7 mm.In addition,increasing the number of FSP was more conducive to obtain the composites with well-formed and microstructural uniformity.The different HEA particulate contents were uniformly distributed,and there were no obvious agglomeration.Excellent HEA particles/Al matrix interfacial bonding was obtained in all composites,and no obvious reaction layer has been found.Rapid cooling underwater has a strong inhibitory effect on the growth of recrystallized grains.With increasing HEA particulate content,the grain size of Al Co Cr Fe Ni/5083Al composite was further refined.When the HEA particulate content was 15 vol.%,the average grain size of the composites was 0.8?m,which was much smaller than the grain size of aluminum alloy(16?m).The results of microhardness test show that the microhardness of composites can be improved by increasing the number of FSP and HEA particulate content.When the HEA particulate content was 15 vol.%,the microhardness of the composites reached a maximum of 147 HV0.2 after 5-pass underwater FSP,which was about 69%higher than that of the aluminum alloy(87 HV0.2).The test results of tensile properties show that the tensile strength and elongation of the composites can be significantly improved by increasing the number of FSP,but the elongation can be reduced due to increasing the HEA particulate content.When the HEA particulate content was 15 vol.%,the ultimate tensile strength and elongation of the composites reached 410 MPa and 16.1%respectively after 5-pass underwater FSP,which was about 41.4%higher than that of the aluminum alloy(290 MPa).The SEM analysis of the tensile fracture shows that the fracture mechanism of the composites was mainly the dissociation fracture of the HEA particles themselves and the pulling out of the particles.The main strengthening mechanisms of composites were the load transfer strengthening,dislocation strengthening and fine grain strengthening.The wear test results show that the wear resistance of the composites was improved with the increase of the HEA particulate content.When the HEA particulate content was 15 vol.%,the wear rate of composites was 85×10-5mm3/m,which was 43%lower than the aluminum alloy(149×10-5 mm3/m).The wear mechanism was transformed from adhesive wear to abrasive wear in the composites with increasing of HEA particulate contents. |
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