The influence of Li on the tensile properties of extruded in situ Al–15%Mg2Si composite

Highlights: ► Effect of Li contents on the microstructure of homogenized and extruded Al–15%Mg2Si. The optimum concentration of Li was found to be 0.5 wt.%. ► The highest UTS and %El. values were 280 MPa and 16 for Al–15%Mg2Si–0.5%Li MMC. ► Li addition changed the fracture behavior of the composite from brittle to ductile. - Abstract: This work was carried out to investigate the effect of different Li concentrations (0.15, 0.3, 0.5 and 0.7) as a modifying agent on the microstructure and tensile properties of an in situ Al–15%Mg2Si composite. Cast, modified and homogenized small ingots were extruded at 480 °C at extrusion ratio of 18:1 and ram speed of 1 mm/s. Various techniques including metallography, tensile testing and scanning electron microscopy (SEM) were used to characterize the mechanical behavior, microstructural observations and fracture mechanisms of this composite. The results showed that 0.5%Li addition and homogenizing treatment were highly effective in modifying Mg2Si particles. The results also exhibited that the addition of Li up to 0.5 wt.% increases both ultimate tensile strength (UTS) and tensile elongation values. However, the tensile results slightly decrease with the addition of more Li (>0.5 wt.%). The highest UTS and elongation values were found to be 280 MPa and 16% for homogenized and extruded Al–15%Mg2Si–0.5%Li composite, respectively. Fracture surface examinations revealed a transition from brittle fracture mode in as-cast composite to ductile fracture in homogenized and extruded specimens. This can be attributed to the changes in size and morphology of Mg2Si intermetallic and porosity content.