Reduced fracturing of intermetallic particles during crack propagation in age hardening Al-based alloys due to PFZs

Based on a shear lag model approach, a simple analytic model for the stress shielding of intermetallic particles due to the presence of a weakened precipitate free zone (PFZ) is derived. The PFZ desensitises the material to the breaking of particles. For the S and θ phase particles in the 2091 aluminium based alloy, particles with average sizes in the range 3–15 μm receive effective shielding from matrix stresses, which raise the matrix stress required to break the particle, and causes a propensity for larger particles to break at smaller applied macroscopic stress.