Fracture behaviour of a magnesium–aluminium alloy treated by selective laser surface melting treatment

• β-Mg17Al12 presents fragile fracture behavior decreasing the ductility of AZ91D.
• SLSM treatment only modifies the β-Mg17Al12 phase whilst α-Mg remains unaltered.
• In-situ SEM bending test allows to observe and data record of the crack propagation.
• Eutectic microestructure of modified β-phase presents ductile fracture behaviour.
• Fracture toughness of laser treated specimen is 40% greater than as-received alloy.

Fracture behaviour of AZ91D magnesium alloy is dominated by the brittle fracture of the β-Mg17Al12 phase so its modification is required to improve the toughness of this alloy. The novel laser treatment named as Selective Laser Surface Melting (SLSM) is characterized by the microstructural modification of the β-Mg17Al12 phase without altering the α-Mg matrix. We have studied the effect of the selected microstructural modification induced by the laser treatment in the fracture behaviour of the alloy has been studied using in situ Scanning Electron Microscopy bending test. This test configuration allows the in situ observation of the crack progression and the record of the load–displacement curve. It has been observed that the microstructural modification introduced by SLSM causes an increase of 40% of the fracture toughness of the treated specimen. This phenomenon can be related with the transition from brittle to ductile fracture behaviour of the laser modified β-phase.