Effect of Mn/Fe ratio on Fe removal efficiency and tensile ductility of an Al–7.0Si–2.4Fe alloy

The poor plasticity of recycled Al–Si alloys severely limits their application owing to the harmful Fe-rich phase. Here we studied the effect of Mn/Fe mass ratio on iron removal efficiency and type of iron-rich phase in Al–7.0Si–2.4Fe alloy. The results show that adding Mn promotes the formation of primary α-Al15(FeMn)3Si2 rather than α-Al8Fe2Si, benefit for the gravity sedimentation and removal of sludge phases owing to the higher formation temperature of α-Al15(FeMn)3Si2. When Mn/Fe ratio is higher than 0.7, a peritectic structure forms showing irregular double-layer band-shape with high Mn/Fe ratio in inner layer, whose volume fraction and size gradually increase with increasing Mn/Fe ratio. The peritectic structures consumed the Mn in the melt, leading to no more increase of Fe removal efficiency. The remaining Mn transforms the needle-like β-Al5FeSi to compact α-Al15(FeMn)3Si2. Both fracture strength and elongation improved significantly compared with the alloy without Mn addition, while mechanical properties have no obviously change with increasing Mn/Fe ratio. There are 10 pictures in this manuscript, the abstracts are listed as follows: Fig. 1 shows the effect of Mn/Fe ratio on the chemical composition of the ingots; Fig. 2 shows the morphologies, chemical composition of the sludge phases in the slag with different Mn/Fe ratios; Fig. 3 shows equilibrium solidification curves with different Mn/Fe ratios; Fig. 4 shows the morphological statistics of the two kinds of typical sludge phases under different Mn/Fe ratios; Fig. 5 shows the effect of sphericity and equivalent diameter on settlement velocity; Fig. 6 shows the microstructure of the Al–7Si–2.4Fe alloy after melt holding under different Mn/Fe ratios; Fig. 7 shows the XRD and DSC curves after melt holding under different Mn/Fe ratios; Fig. 8 shows the morphological characteristics of Fe-rich phases in different spatial directions; Fig. 9 shows the tensile properties of the as-cast alloy with different Mn/Fe ratios; Fig. 10 shows the cracks initiation and propagation of the as-cast alloy with different Mn/Fe ratios.