Study On Hot Extrusion-Hot Rolling Processing And Properties Of 7075Al Matrix Composites Reinforced By AlSiTiCrNiCu High Entropy Alloy

The research on the mechanism of strengthening and toughening aluminum matrix composites reinforced by particles becomes one of the hotspots at present.High entropy alloys(HEAs),new reinforcements,have good interfacial wettability with the matrix.It can improve strength and toughness at the same time,so it is a kind of reinforcement with excellent application prospect.At present,there are few concerns about the forming process of high-entropy alloys particles reinforced aluminum matrix composites and there are less reports on its subsequent processing technology.Therefore,this article will mainly study the effects of hot extrusion and hot rolling process on microstructure and mechanical properties of aluminum matrix composites with high entropy alloy particles.In this paper,AlSiTiCrNiCu high entropy alloy particles as reinforcements and 7075Al as the matrix were used.Aluminum composites reinforced by HEAs particles were fabricated by powder hot extrusion.Microstructure and mechanical properties of the composites with different hot rolling process parameters were tested and analyzed by scanning electron microscopy(SEM),transmission electron microscopy(TEM),high resolution transmission electron microscopy(HRTEM),hardness tester,and tensile tester.Effects of high entropy alloys volume fraction and hot rolling process parameters,such as hot rolling temperature and rolling deformation extent on the microstructure,interface characteristics and mechanical properties of aluminum matrix composites reinforced with high entropy alloys particles were studied.High-entropy alloys particles were fabricated by mechanical alloying with uniform composition.The theoretical density of AlSiTiCrNiCu high entropy alloy was 5.76×10~3 kg/m~3and a single-phase BCC structure was formed.In addition,the HEAs particles were irregular in shape and the particle size was d(0.5)=12.20μm.(AlSiTiCrNiCu)_p/7075Al composites were fabricated by hot-extrusion.It revealed that HEAs particles were uniformly distributed in the matrix alloy.TEM analysis showed that the interface between AlSiTiCrNiCu and Al matrix was a diffusion-type interface and no interfacial reaction product was found.Thus,(AlSiTiCrNiCu)_p/7075Al composites have good tensile strength and elongation.As the volume fraction increased,its tensile strength gradually increased and its elongation decreased.In the hot extrusion process,on one hand,the tensile strength and elongation of the composites increased with increasing the extrusion temperature and extrusion ratio.On the other hand,the tensile strength of the composites increased with increasing the cold pressing pressure while the elongation decreased.In this paper,the tensile strength of 5vol.%(AlSiTiCrNiCu)_p/7075Al composites reached 509.3 MPa(P=200MPa,T=400℃,λ=17.36)and the elongation reached 9.78%(P=100MPa,T=450℃,λ=17.36).In the hot rolling process,when the hot rolling temperature was 440°C and the rolling deformation extent was certain,the mechanical properties of(AlSiTiCrNiCu)_p/7075Al composites were optimal at the volume fraction 5 vol.%.When the hot rolling temperature was certain,the tensile strength and hardness of 5 vol.%(AlSiTiCrNiCu)_p/7075Al composite increased with increasing hot rolling deformation extent while the elongation decreased.When the rolling deformation was the same(ε=60%),the distribution of high-entropy alloy was uniform and the comprehensive property of(AlSiTiCrNiCu)_p/7075Al composite at 410°C was optimal,whose tensile strength and elongation reached 506.5 MPa and 5.34%.When the hot-rolling temperature increased furthermore,more cracks were observed in the high-entropy alloy particles as a result of the decresed tensile strength and elongation.The fracture of Al composites reinforced with AlSiTiCrNiCu high entropy alloys particles occurred by mixed mechanism,such as high entropy alloys particles cracking,high entropy alloys and matrix peeling and the matrix ductile tearing(tearing edges and dimples).