If strips of aluminium and steel are fixed together on metallic strip and both are heated then $\left(\alpha_{\mathrm{Al}}>\alpha_{\text {steel }}\right)$ aluminium will exapnd more because the metallic strip with higher coefficient of linear expansion $\left(\alpha_{\mathrm{Al}}\right)$ will expand more Thus it should have larger radius of curvature. Hence, aluminium will be on convex side.