Effect of Cu content on the microstructure evolution and fracture behavior of Al–Mg–Si–xCu (x = 0, 1, 2 and 4 wt.%) alloys

Abstract

Lightweighting automobiles can dramatically reduce their consumption of fossil fuels and the atmospheric CO2 concentration. Heat-treatable Al–Mg–Si has attracted a great deal of research interest due to their high strength-to-weight ratio, good formability, and resistance to corrosion. In the past, it has been reported that the mechanical properties of Al–Mg–Si can be ameliorated by the addition of Cu. However, determining the right amount of Cu content still remains a challenge. To address this the microstructure evolution, phase transformation, mechanical properties, and fracture behavior of Al–Mg–Si–xCu (x = 0, 1, 2 and 4 wt.%) alloys were studied through optical and field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy, differential scanning calorimetry, hardness measurements, and tensile tests. The obtained results indicate that the addition of Cu of up to 4 wt.% improved the hardness (17.5% increase) of the alloy, but reduced its ductility. Moreover, an alloy with 4 wt.% Cu fractured in a brittle manner while Al–Mg–Si showed ductile fracture mechanism. In addition, differential scanning calorimetry analysis revealed five exothermic peaks in all Cu containing alloys. Our results also showed that θʹ and Qʹ-type intermetallic phases formed owing to the addition of Cu, which affected the strength and ductility. Thus, Al–Mg–Si–xCu alloy with the right amount of Cu content serves as an excellent candidate for replacing more costly alloys for cost-effective lightweighting and other applications.