Effects of damaged coarse inclusion particles on mechanical properties of wrought aluminum alloys

In-situ SEM observation of fracture toughness tests has been used to characterize the fracture behavior of a wrought aluminum alloy. Particular attention is given to in-situ fracture strength of the coarse inclusions associated with this alloy. The fracture domain of CuAl₂ and Al₂CuMg particles with respect to the main crack is also investigated. Crack propagation is conducted by ductile failure of matrix ligaments between the fractured particles and the main crack, thereby producing slight crack deflection. Coarse Al₃Zr and Al₃Ti particles even adjacent to the fracture surface remain intact, while CuAl₂ and Al₂CuMg particles are extensively damaged ahead of a crack-tip. A combination of HRR singularity and Eshelby type internal stress analysis is used to estimate the in-situ strength values of various inclusion particles. It is concluded that the fracture strength of the inclusion particles has strong dependence on diameter. For example, it decreases from 740 to 500 MPa for the Al₂CuMg. By decreasing the volume fraction of the coarse inclusions larger than 3μm from 2.2 to 1.2% by applying various heat and thermo-mechanical treatments, 0.2% proof stress, fracture toughness and crack propagation resistance of the alloy are remarkably improved without sacrificing ductility.