Interface Microstructure and Mechanical Properties of Al/Steel Bimetallic Composites Fabricated by Liquid-Solid Casting with Rare Earth Eu Additions

To improve the Al/Steel bimetallic interface, Eu was firstly added to the Al/Steel bimetallic interface made by liquid-solid casting. The effects of Eu addition on the microstructure, mechanical capacities, and rupture behavior of the Al/Steel bimetallic interface was studied in detail. As the addition of 0.1 wt.% Eu, the morphology of eutectic Si changed from coarse plate-like to fine fibrous and granular in Al-Si alloys, and the average thickness of the intermetallic compounds layer decreased to a minimum value of 7.96 μm. In addition, there was a more sudden drop of Fe in steel side and the Si in Al side was observed to be more than the other conditions. The addition of Eu did not change the kinds of intermetallic compounds in the Al/steel reaction layer, which was composed of Al(5)Fe(2), τ(1)-(Al, Si)(5)Fe(3), Al(13)Fe(4), τ(5)-Al(7)Fe(2)Si, and τ(6)-Al(9)Fe(2)Si(2) phases. The addition of the element Eu did not change the preferential orientation of the Al(5)Fe(2), τ(1)-(Al, Si)(5)Fe(3), Al(13)Fe(4), τ(5)-Al(7)Fe(2)Si, and τ(6)-Al(9)Fe(2)Si(2) phases, but refined the grain size of each phase and decreased the polar density of Al(5)Fe(2) phase. Eu was mainly enriched in the front of the ternary compound layer (τ(6)-Al(9)Fe(2)Si(2)) near the Al side and steel matrix. The Fe and Al element distribution area tended to narrow in the interface after the addition of 0.1 wt.% Eu, which is probably because that Eu inhibits the spread of Al atoms along the c-axis direction of the Al(5)Fe(2) phase and the growth of Al(13)Fe(4), τ(5)-Al(7)Fe(2)Si, and τ(6)-Al(9)Fe(2)Si(2) phases. When the Eu content was 0.1 wt.%, the shear strength of the Al/Steel bimetal achieved a maximum of 31.21 MPa, which was 47% higher than the bimetal without Eu.