The role of thickness on the fracture behavior of Al/Mg–Li/Al composite processed by cold roll bonding

Abstract

This paper aims to study the microstructure, fracture behavior, and other mechanical properties of a three-layered Al/Mg–Li/Al composite fabricated by the cold roll bonding (CRB) process. Alloying Mg with Li gave a double-phase magnesium-lithium alloy with high ductility, strengthened by bonding to two Al layers. By conducting CRB, the thickness of the composite reduced from 3 mm in the first stage to 1 mm in the last one, and in between, the mechanical and microstructural properties in five different thicknesses (2, 1.8, 1.6, 1.2, and 1 mm) were investigated. Grains were elongated in the rolling direction (RD) according to the pictures prepared by the optical microscope, and this elongation grows as the thickness of the composite reduces. Studying the mechanical properties, including the UTS, total elongation, and fracture behavior in two directions: rolling direction and traverse direction (TD), showed that UTS increases as the thickness decreases and is higher for TD samples in comparison to RD ones. Total elongation decreases by reducing the thickness, but for RD samples, it was lower than TD ones. The results show that both applied strain and thickness affect the fracture toughness simultaneously. The highest amount of fracture toughness does not belong to the sample with the highest thickness or the one that undergoes the highest strain during the CRB. For RD samples, the highest fracture toughness was recorded at the thickness of 1.6 mm, while for TD ones, it was at the thickness of 1.2 mm. SEM images of the fractured layers confirm the presence of dimples which are the reason for the ductile fracture, and this ductility reduces as the thickness goes down.