Evolution of grains to relieve additional compressive stress developed in Al–Mg alloy films during thermal annealing

• Mechanism for grain evolution in Al–Mg alloy films
• The featureless, dense cross-sectional microstructure of the as-deposited films
• A grainy microstructure after the thermal annealing
• Interplay between the microstructure and residual stress

In this work, a possible mechanism for grain evolution in Al–Mg alloy films during thermal annealing is suggested on the basis of the phase transition and the related residual stress. Al–Mg alloy films with compositions of 14.0 and 18.0 wt.% Mg content were deposited on cold-rolled steel substrates by the direct current co-sputtering method using Al and Mg targets. After the deposition, the samples were thermally annealed at 400 °C for 10 min. The featureless, dense cross-sectional microstructure of the as-deposited films turned into a grainy microstructure after the thermal annealing. According to the residual stress evaluated by using the X-ray diffraction (XRD)-sin2ψ technique and the phase analysis by XRD, it is likely that grains were created in order to relieve the additional accumulation of residual stress originating from the phase transition from face-centered cubic Al (α) to Al3Mg2 (β) and Mg (δ) phases, suggesting an interplay between the microstructure and residual stress.