Microstructure and mechanical property evolution of additive manufactured eutectic Al-2Fe alloy during solidification and aging

Abstract

This study presents the microstructure and mechanical properties of an additive manufactured recyclable Al-2Fe alloy fabricated by laser powder bed fusion (LPBF). The microstructure evolution of the Al-2Fe alloy aged at elevated temperatures and its impact on the mechanical properties were systematically investigated. Firstly, the single melt scanning experiment verified that Al-Al6Fe anomalous eutectic structure was initially formed from the liquid phase. Secondly, the as-built Al-2Fe contains nano-size and rod-shaped Al6Fe particles which uniformly dispersed in a supersaturated Al matrix. The Al6Fe particles with an average diameter of ~89 nm shows a coherent crystallographic relationship with the matrix as (046)Al6Fe // (2¯02¯)Al, and [032¯]Al6Fe // [1¯11]Al. The ultimate tensile strength and total elongation of 287.0 MPa and 12.0% were obtained in the ultrafine as-built Al-2Fe, respectively. Aging at elevated temperatures made the Al6Fe particles coarsened and transformed into Al13Fe4 particles at 350 °C. The amount of the total Al-Fe intermetallic compounds (Al6Fe+Al13Fe4) increased with the aging temperature due to the precipitation of the supersaturated Fe atoms. It exhibits a slow increase in grain size and a decrease in dislocation density in the Al-2Fe samples with the increase of aging temperature. All Al6Fe particles were transformed into coarse Al13Fe4 particles at 550 °C. Thirdly, the quantitative analysis indicates that the dominant contribution to the yield strength derives from the dispersion strengthening mechanism by creation of fine Al6Fe and Al13Fe4 particles. The results in this work demonstrate that ultrafine microstructure can be obtained in a simple binary Al-Fe alloy as a result of the extremely high cooling rate during LPBF process, which offers a design strategy towards high-strength recyclable aluminum alloys.