The effect of solid-state process and heat treatment on the fatigue life of RHA-reinforced AA6061 chip-based recycled composite

The direct recycling method has gained increasing attention due to its potential to reduce waste and costs while being environmentally friendly. This study investigated the effect of hot extrusion and heat treatment on AA6061 aluminium chips recycled and reinforced with 5 wt.% rice husk ash (RHA) burned at 1100 ℃. The cold compacted billets were preheated at 550 ℃ for 2 h before being extruded at 300 ℃. Half of the extruded billets were heat treated for 2 h at 530 ℃, rapidly quenched in water at 26 ℃, and then underwent artificial aging at 175 ℃ for 4 h. The samples were tested for relative density, ultimate tensile strength (UTS), hardness, and fatigue life, and examined for microstructure. Comparisons were made between heat-treated, untreated, and the as-received samples. The highest strength of 145.65 MPa, hardness of 64.78 HV, and density of 2.64 g/cm³ were observed in the treated samples. Heat-treated samples recorded higher fatigue limits than non-treated ones. Basquin's equation was used to predict the fatigue life of the composite at an untested stress amplitude. Energy dispersive spectroscopy (EDS) analysis revealed that treated samples constitute 83.29% of the total composition, followed by magnesium at 7.32%, and oxygen at 6%. Atomic force microscopy (AFM) analysis showed that the grain length of the heat-treated sample ranged from 0.792 to 0.894 µm, which is larger than the grain size of the untreated samples. In conclusion, hot extrusion and heat treatment effectively improve the microstructure and mechanical properties of the chip-based RHA-reinforced composite.