Peak hardness stability analysis of Al7075 alloy dispersed with Ni coated duralumin powder during natural aging phenomena

This technical paper presents the successful reinforcement of nickel (Ni) coated duralumin powder in an Al7075 matrix using the liquid stir casting technique and property stability obtained by heat treatment. Ni coating is performed by electroless nickel plating technique where 8 μm coating thickness was observed to be the minimum required to prevent dissolution of the reinforcements (duralumin powder) in the matrix (Al7075). During stir casting it was observed to uniformly disperse the coated duralumin powder up to 7 wt.%. Al7075 alloy and composites were artificially aged with solution heat treatment (SHT) performed at 450 °C for 4 h, water quenched and then aged at 120, 150 and 180 °C. Al7075 alloy and composites were naturally aged for 24 weeks in atmospheric temperature after peak aging. Composites aged at 120 °C exhibited superior results and considered as optimum aging temperature compared to those aged at 150 and 180 °C. Peak hardness values in 7075-7Dp+8T composite improved by 108% and 7075-7Dp+10T composite improved by 110% when compared to peak aged (at 120 °C) Al7075 alloy. Moreover, composites with coated reinforcement displayed a higher resistance to natural aging, with reductions of 53.5 and 54.4% in natural aging tendency compared to the naturally aged Al7075 alloy for 7075-7Dp+8T and 7075-7Dp+10T composites respectively. However, an increase in Ni coating thickness beyond the optimal 8 μm did not significantly improve as cast and peak hardness or natural aging resistance. XRD analysis confirmed that there is presence of CuAl2, CuAl2Mg, Mg2Si, and MgZn2 phases in peak-aged (120 °C) 7075-7Dp+8T sample. Considering the limited impact on property enhancement and the financial burden associated with thicker coatings, a coating thickness of 8 μm is recommended as compared to 10 μm.