Development of high strength aluminum alloys and aluminum matrix composites for structural application using solid state processing

Abstract

In recent decades, aluminium alloys have been widely used in aerospace, automotive, and other structural applications. Although aluminium has a low density, the effective use of these alloys is constrained by their poor tensile strength, hardness values, and wear and fatigue characteristics. Friction stir processing (FSP) is one of the most effective ways to increase mechanical properties by refined grain size. The grain refinement can be further improved by tool pin eccentricity and cooling rates. The current study mainly focused on the FSP of AA 6063 alloys with different pin eccentricities (0 mm and 0.6 mm) under different cooling rates. Results showed that the FSP using a tool with 0.6 mm pin eccentricity and a higher cooling rate improved the hardness, tensile strength, fretting wear resistance, and corrosion resistance of AA6063 alloy. Pin eccentricity and increased cooling rate reduce the peak temperature during FSP, resulting in fine grain structure and enhanced mechanical properties. The mechanical properties of AA6063 can also be enhanced by making aluminium matrix composites (AMCs). Different types of reinforcement can affect the strength and ductility of a material in various ways. For example, the use of hard ceramic reinforcement can increase tensile strength but decrease ductility, whereas metallic reinforcement can enhance ductility while only slightly improving strength. Hence, an attempt was made to develop AA6063 matrix composites (AMCs) using ZrO2 and nickel particles (with different wt.%) as reinforcement through the FSP route. The microstructural features of AMCs revealed that the equiaxed refined grains were due to dynamic recrystallization and pinning effect. The ductility improved while the tensile strength decreased with an increase in the percentage of nickel in hybrid reinforcement.