Comparison of fracture in sheets of low pressure gas (LPG) steel and aluminium alloys

Fracture behaviour under different stress states of four heats of hot rolled low pressure gas (LPG) grade steel and three 1 mm thick cold rolled aluminium alloys (Al–Cu–Mg, Al–Mg and Al–Mn) is compared. Dimple fracture was present in all four materials but the dimples were larger and of more uniform size in LPG steel compared with those present in the Al-alloys. Depending on the relative strength of pearlite and pearlite–matrix interface, failure in LPG steel was either transgranular or ductile intergranular. In the Al-alloys, particle–matrix decohesion was always responsible for dimple formation and transgranular fracture. In the Al–Cu–Mg and Al–Mg alloys a bimodal dimple size distribution, traceable to precipitates of two different sizes, was present but in the Al–Mn alloy the dimple size was larger and of nearly the same size. The results are explained in terms of composition, microstructure and mechanical properties of the alloys.