Fabrication of AZ91D/Cu/Mg2Cu and AZ91D/Mg2Cu/MgCu2/MgO in-situ hybrid surface nanocomposites via friction stir processing

Abstract

In this study, in situ surface nanocomposites based on Mg-CuO and Mg-Cu systems were developed via six passes of friction stir processing (FSP) on the surface of AZ91 magnesium casting alloy. In-situ phase evolution during FSP with the addition of Cu and CuO micro-powders was studied by x-ray diffraction (XRD) analysis and microstructural investigations. Here, AZ91/Cu nanocomposite was reinforced by the in situ formation of Mg2Cu intermetallic compound. In AZ91/CuO nanocomposite, CuO particles were reduced and MgO and MgCu2 reinforcing particles alongside Mg2Cu intermetallic compounds were formed during FSP. Grain refinement and in situ formation of reinforcement particles with different sizes ranging from nano- to micro-scale significantly improved mechanical performance of the specimens. Dynamic recrystallization was found to be the main mechanism of grain refinement. After six passes of FSP, the hardness values of AZ91/Cu and AZ91/CuO nanocomposites were increased by 69.1% and 91%, respectively. Besides, AZ91/CuO nanocomposite exhibited the best tensile strength and wear resistance among all the samples. The dominant wear mechanisms were abrasive and delamination wear in AZ91 magnesium alloy, while nanocomposite specimens were worn mainly by abrasive mechanism.