The strengthening contribution of graphene platelets in AlSi7Mg/graphene composite fabricated via laser powder bed fusion

Manufacturing graphene-reinforced aluminum composites by laser powder bed fusion (LPBF) attracts expanding interests for the prospective significant strengthening of aluminum alloys allowed by the superior mechanical properties of graphene and the advantages of LPBF in rapid net-forming. However, the achievable strengthening contribution of graphene in LPBF Al/graphene composites remains obscure, as vastly varying performances of as-built Al/graphene composites have been reported for the processing complexities in mixing graphene platelets into Al alloy powders and subsequent LPBF. To unravel the contribution of graphene, AlSi7Mg alloy and AlSi7Mg/graphene (0.1 wt%) composite were prepared by LPBF and further treated by solution-and-ageing (SA) to dissolve the fine Al-Si eutectic networks along boundaries of cellular α-Al grains and the Si nanoparticles inside cellular α-Al grains which are the main strengthening sources in as-built AlSi7Mg alloy and AlSi7Mg/graphene composite. Microstructure characterization indicates no significant change induced by graphene addition in AlSi7Mg alloy both before and after SA treatment. Tensile tests on as-built AlSi7Mg alloy and AlSi7Mg/graphene composite show almost identical yield strength (260–270 MPa), ultimate tensile strength (440–445 MPa), and total elongation (14%-16%), while the results of SA-treated AlSi7Mg alloy (335 MPa) and AlSi7Mg/graphene composite (363 MPa) show an increment of ∼28 MPa in ultimate tensile strength but similar yield strength (260 MPa) along with slightly increased total elongation (from 13.4% to 16%), which demonstrates the strengthening contribution of graphene (0.1% wt.) in the strain-hardening of SA-treated AlSi7Mg/graphene composite. These observations would help to understand the strengthening effect of graphene in aluminum/graphene composites.