Scandium Canada Ltd V.SCD

Alloying effect of Sc on the Aluminum die casting alloys

[ScandiumPower]

Abstract

The alloying effects of small additions of Sc, Zr, Cr on the microstructure and mechanical properties of Al-5Mg-2Si casting alloys produced by High Pressure Die Casting (HPDC) were investigated. The microstructure of the Al-alloys consists primarily of the α-Al and Al-Mg2Si eutectic cells and the α-Al15(Mn,Fe)3Si2 intermetallic phase as well as coarse Al7Cr and Al3Zr intermetallic phases. The most significant improvement in the mechanical properties was achieved in the alloys with Sc + Cr and Sc + Zr additions. Alloying with 0.2 wt% of Sc in combination with Zr and Cr additions exhibits the best combination of strength and ductility with a yield strength of 206 MPa, an ultimate tensile strength of 353 MPa and an elongation of 10% in the as-cast condition. Alloys with Cr + Zr addition have a higher hardness and tensile strength compared to the AlMg5Si2Mn base alloy (commercially known as “Magsimal-59”) and the similar levels of yield strength and elongation. However, they have lower levels of all set of properties compared to the alloys with Sc + Cr and Sc + Zr additions, due to the presence of coarse Al7Cr sludge and Al3Zr intermetallic phases

....

Conclusions

The tensile properties of new alloys, as well as nanohardness of the Al3Zr and Al7Cr intermetallic phases, have been studied. Moreover, the segregation of Cr, Zr and Sc in Al-Mg-Si-Mn alloys has been shown. The Al7Cr intermetallic phases have been detected in the alloys with Cr + Zr and the Al3Zr intermetallic phases have been detected in the alloys with Cr + Zr and Sc + Zr additions. ILS in the alloys with Sc additions is reduced by a factor of 4 compared to the base alloy, whereas in the alloys with the Cr + Zr additions only a small reduction of the ILS was observed. No other changes in the structure were observed.

The Al3Zr phase has an orthogonal shape with an average size of 7.1 ± 2.80 μm, which slightly changes in the SZ-series of alloys, becoming more coarse with the average size close to hundreds of micrometres. Whereas the Al7Cr phase has an irregular blocky-like shape and sizes 17.5 ± 5 μm. The Al3Sc phase with irregular shape has been observed in the interdendritic space of the alloys with Sc + Zr and Sc + Cr additions. The high volume fraction of the Al7Cr and Al3Zr intermetallic phases (in the CZ22 alloy) leads to the degradation in the tensile strength and elongation to failure. However, in spite of the fact that Al3Zr phase is large compared to the Al7Cr phase, it does not negatively affect the mechanical properties as Al7Cr. Sc + Zr and Sc + Cr additions have the most prominent effect on mechanical properties. Even concentrations of only 0.1 wt% of both alloying elements lead to the significant increase of the tensile properties. Thus the yield strength of SC11 alloy is equal to 190 MPa, whereas for SZ11 this value is 201 MPa. At the same time elongation to failure of SC11 is equal to 10.6% and 9.8% for SZ11 respectively. Nonetheless, the mechanical properties of the SZ and SC-series are on the same level as compared to the alloys with the single addition of Sc in an amount of 0.1 wt%.

https://www.sciencedirect.com/science/article/pii/S1044580320320088