In-situ fabrication of submicron α-Al₂O₃ particle reinforced AlSi9Cu3 alloy matrix composites by TIG arc process

In this paper, the fabrication of submicron α-Al₂O₃/Al composites from Al-SiO₂ system by tungsten inert gas (TIG) arc processing technology was investigated and the submicron α-Al₂O₃/AlSi9Cu3 composite was prepared by dilution and ultrasonic electromagnetic coupling treatment. The microstructures, phase analysis and mechanical properties of the composites were characterized by optical microscope (OM), scanning electronic microscopy (SEM), energy dispersive spectrometer (EDS), x-ray diffraction (XRD), tensile and microhardness testing, respectively. The results revealed that the morphologies and distribution of α-Al₂O₃ and silicon was significantly affected by the TIG arc current. With the optimum current (120 A), the in situ reaction was complete, the substituted Si phase was presented in rod-shape or needle-shape and agglomerated at the α-Al grain boundary to form Al-Si eutectic phase, and the grain refinement of α-Al phase was the most obvious. The average size of generated α-Al₂O₃ particles was about 500 nm, while these particles mainly distributed uniformly along the α-Al grain boundary. Ultrasonic and electromagnetic treatments could promote the uniform distribution of α-Al₂O₃ particles in the AlSi9Cu3 matrix, while these particles could affect the formation of α-Al dendrites and decrease the secondary dendrite arm spacing from 19.8μm to 10.4 μm. The tensile strength, elongation, and microhardness of the α-Al₂O₃/AlSi9Cu3 composite with 5vol % particles yielded 282 MPa, 5.8%, and 127HV, respectively. Compared with those of the matrix alloy, they increased 17.9%, 23.4%, and 45%, respectively. (paper)