High as-cast strength die-cast AlSi9Cu2Mg alloy prepared by nanoparticle strengthening with industrially acceptable ductility

Abstract High as-cast strength die-cast AlSi9Cu2Mg alloy was achieved with industrially acceptable ductility, via the addition of titanium diboride nanoparticles. The main intermetallic compounds in the die-cast AlSi9Cu2Mg alloy were identified as θ–Al2Cu and Q–Al5Cu2Mg8Si6 phases. The Fe-rich compound formed in the present die-cast alloy with a high Mn/Fe ratio of 3:1 was determined as the BCC structured α–Al15(Fe,Mn)3Si2 phase with a lattice parameter of a = 1.2702 nm, and the Fe-rich compound had highly faceted morphology with {110} surface termination. The Al matrix phase in the die-cast AlSi9Cu2Mg alloy was refined by ∼65% from 18.1 μm to 6.4 μm, after adding 3.0 wt% titanium diboride nanoparticles. The titanium diboride nanoparticles in the alloy showed coherent interface with the Al matrix, with the (11-1) lattice face of Al parallel to the (0001) lattice face of titanium diboride. The as-cast AlSi9Cu2Mg alloy containing 3.0 wt% titanium diboride nanoparticles exhibited the high yield strength of 233 ± 3 MPa and the tensile strength of 398 ± 7 MPa, as well as the industrially acceptable elongation of 4.8 ± 0.7%, and it showed at least 23% improvement in the as-cast yield strength over the existing die-cast Al alloys. The strengthening by nanoparticle and coherent interface (∼32 MPa) was higher than that by the refining of Al matrix (∼10 MPa). The addition of titanium diboride nanoparticles also affected the fracture of the die-cast AlSi9Cu2Mg alloy, and cracks were prone to form in the Q and Fe-rich compounds, after the addition of titanium diboride nanoparticles.