Strength and fracture of aluminium alloys

It is general that dimple type fracture initiating from inclusions or second phase particles dominates the overall fracture behaviour of practical aluminium alloys; it is important to assess the fracture strength levels of such particles in a quantitative manner. In the present article, three different types of aluminium-based materials are discussed; wrought aluminium alloys including both middle and high strength types, AI-Si type casting alloys and discontinuously-reinforced composites (DRC). The effects of coarse particles on the fracture characteristics of the alloys are analysed considering elasto-plastic stress singularity and Eshelby type internal stress analyses. For example, the in-situ strengths of CuAl2 and Al2CuMg intermetallics which are typically observed in an A2091 Al-Li alloy are estimated at about 710 MPa, while those of the modified eutectic Si particles in an Al-Si casting alloy varies between 500 to 900 MPa. It is also interesting to note the much lower strengths (i.e., typically 200 MPa) of coarse primary Si particles. In addition, according to the fracture-mechanical simulation and numerical analysis for the fracture and strengthening of DRCs, it has been clarified that some aggregated reinforcement granules clearly provide the superior combination of strength and toughness with this interesting behaviour then being utilized for the novel design of advanced DRCs recently.