Investigating the microstructure and mechanical properties of Al–Ag-Sc ultra-fine grain alloy processed by accumulative rolling bonding method

Abstract

The aim of the present study is to investigate the effect of accumulative roll bonding (ARB) and precipitation hardening on the microstructure development and there of mechanical properties of ultrafine grained Al–Ag-Sc alloy. For this purpose, the samples were heated to a temperature of 600 °C for 24 h, and then they were quenched in water. In order to carry out the two-stage precipitation hardening process, the samples were placed in the furnace at a temperature of 350 °C for 5000 s in the first stage, which was followed by quenching in water. In the second stage, they were heated to 250 °C for 5000 s following by water quenching too. Following, the samples were subjected to the ARB for up to 8 cycles. Scanning Electron Microscope (SEM) equipped with Electron Backscatter Diffraction (EBSD) and energy dispersive spectroscopy (EDS) techniques, and X-Ray Diffraction (XRD) was used to verify the microstructure and phase analysis of the prepared samples. Also, tensile and microhardness tests were conducted to confirm the mechanical properties, and pin-on-disk tests were done to check wear behavior. Microstructural parameters such as crystallite size, microstrain, and density of dislocations in rolled sheets were estimated using the Rietveld method. The Results have shown that applying various cycles of the ARB process leads to the development of ultra/nano grain structure. In that sense, performing 8-cycle of the ARB transformed the low angle grain boundaries (LAGBs) of the 4-cycle ARB condition to high angle grain boundaries (HAGBs). Results showed that there is proper welding between different layers, except for the layers created in the last cycle. Similarly, the obtained size of the crystallites demonstrates that the samples become finer when ARB cycles are increased. The results of the mechanical tests indicated that after 8 cycles, there is approximately 3.5-fold and 2.5-fold increase in the tensile strength and hardness compared to the original (annealed) sample, respectively. While the elongation decreased slowly and reached 1.5% in the 8th cycle. A fractography of the fracture surface of the original sample included deep and coaxial dimples, indicating a ductile fracture. Analysis of wear surface degradation showed that scratch wear occurred for all samples.