Effect of Mn and cooling rates on α-, β- and δ-Al–Fe–Si intermetallic phase formation in a secondary Al–Si alloy

Abstract

Secondary Al-Si alloys Al7.1Si(1.5-x Mn )Fe(x Mn )Mn with x Mn = 0, 0.3, 0.375, 0.6, 0.75 at.% have been solidified with different cooling rates: 0.05 K/s, 1.4 K/s, 11.4 K/s and 200 K/s. In the ternary alloy with x Mn = 0 at.%, formation of the primary α h phase is suppressed upon higher cooling rates at the cost of formation of plate-shaped β and δ phase particles. In the quaternary alloys, with increasing Mn content, α c -phase particles with Chinese-script morphology form and replace the plate-shaped intermetallic particles. While the α c phase forms at intermediate cooling rates only, plate-shaped particles additionally form at low and high cooling rates. The β phase dominates after solidification with lower cooling rates and the δ phase dominates upon higher cooling rates in the plate-shaped particles. The kinetic effect in terms of solidification rate and the chemical composition effect on the phase selection of Fe-containing intermetallic particles in the alloys along the solidification path have been discussed.

Precipitation Hardening at Elevated Temperatures above 400 °C and Subsequent Natural Age Hardening of Commercial Al–Si–Cu Alloy

“…These results demonstrate a microstructure composed of α-Al 15 (Fe, Mn) 3 Si 2 (bright contrast) and Si (intermediate-contrast) phases in the α -Al matrix of the solution-treated samples. The observed morphology of the α-Al 15 (Fe, Mn) 3 Si 2 phase corresponds well with the results of previous studies on commercial Al cast alloys [ 10 , 11 , 12 , 13 , 29 , 30 ]. In addition, no clear diffraction peaks derived from the β-Al 9 Fe 2 Si 2 phase [ 31 ] were detected in the 520 °C solution-treated sample ( Figure 5 a) and subsequently aged samples ( Figure 5 b,c), indicating a slight formation of a β-Al 9 Fe 2 Si 2 phase in the studied AC2B alloy samples.…”

“…In the Al–Si–Cu–Fe quaternary system ( Figure 12 b), the Fe-rich intermetallic β-AlFeSi phase (τ 6 -Al 9 Fe 2 Si 2 ) [ 31 ] appears below approximately 560 °C and in equilibrium with the other solid phases (α-Al, Si, and θ-Al 2 Cu phases) at lower temperatures. The calculated results indicate that a trace amount (0.4% mass) of Fe (as an impurity) could enhance the formation of the β phase in Al–Si–Cu alloys, which is in good agreement with the results in previous reports on conventional Al–Si–Cu alloys [ 13 , 30 ]. The thermodynamic calculation for the Al–Si–Cu–Fe–Mg system ( Figure 12 c) assessed the formation of the Q-Al 4 Cu 2 Mg 8 Si 6 phase [ 33 ] in the AC2B alloy composition containing a small amount of Mg (0.4% mass) at temperatures below approximately 470 °C, which corresponded well with the needle-shaped precipitates observed in the sample aged at 400 °C ( Figure 8 and Figure 9 ).…”

Effect of Substrate Plate Heating on the Microstructure and Properties of Selective Laser Melted Al-20Si-5Fe-3Cu-1Mg Alloy

“…Once the nucleation of δ-Al 4 FeSi 2 phase takes place, both Fe and Si elements diffuse to the edge of δ-Al 4 FeSi 2 phase because of the decreasing solubility of these two elements in α-Al matrix [ 61 ], promoting further growth of δ-Al 4 FeSi 2 phase with one fast growth direction and two slow directions, which contributes the needle-like morphology. Subsequently, δ-Al 4 FeSi 2 phase will be transformed into β-Al 5 FeSi phase [ 62 ], which can be accomplished via the diffusion of Fe and Si atoms from δ-Al 4 FeSi 2 phase to α-Al matrix. However, low diffusion coefficients of Fe and Si atoms in α-Al matrix (D Fe = 7.923 × 10 −14 m 2 /s and DSi = 1.524 × 10 −12 m 2 /s at 883 K, calculated according to [ 63 ]).…”

Interaction of Fe‐Containing, Secondary Al–Si Alloy with Oxide and Carbon‐Containing Ceramics for Fe Removal

“…The β and δ phase form plate‐shaped particles, whereas the α h and α c phase form polyhedral particles during slow cooling. [ 20 ] Removing the primary Fe‐containing particles reduces the Fe content in the Al–Si alloy. [ 21–27 ] Their formation can be facilitated by melt conditioning.…”