Zr and Si co-substitution for SmCo7 alloy with enhanced magnetic properties and improved oxidation and corrosion resistances

The effects of Zr and Si co-substitution on the magnetic properties, oxidation and corrosion resistances of TbCu7-type Sm-Co alloys have been investigated. Zr addition is very effective in promoting the formation of TbCu7-type structure and it contributes to the most of the coercivity enhancement. The largest coercivity of 1389 kA/m was obtained for SmCo6.3Zr0.4Si0.3 alloy. Si addition can significantly improve the oxidation resistance. After exposure in air at 500 °C for 90 h, the thickness of the oxidation layer was just 106 μm for as-cast SmCo6.4Zr0.3Si0.3 alloy compared to 230 μm for the SmCo6.7Zr0.3 alloy. The room temperature coercivity of SmCo6.4Zr0.3Si0.3 ribbon is as high as 884 kA/m after exposure at 300 °C in air for 10 min. The improved corrosion resistance for Si added alloys was also confirmed by polarization curve measurement. Zr and Si co-substitution provides a good approach for enhancing both the coercivity and resistances to oxidation and corrosion of the TbCu7-type Sm-Co alloy.