Analysis of the reasons for the peeling of sand cast aluminum castings

Analysis of the reasons for the peeling of sand cast aluminum castings:

(1) The local surface compactness is not good, and the partial peeling is caused by the failure of the compact layer under the action of external force due to insufficient surface compactness or poor meshing of the local die casting.

(2) The microscopic morphology of the cold barrier. The microscopic morphology of the cold barrier refers to the discontinuous or uneven filling of the metal liquid due to the pressure change during die casting. When the temperature of the local mold is low, a small amount of liquid that enters the cavity hits the mold wall and solidifies into a skin layer. The skin layer will be quickly formed into a thin metal layer by water vapor and oil fume, and then the entering liquid metal will be covered and solidified on the surface. Then the layer interface is formed. Due to the phenomenon of the interface of this layer, the bonding strength with the matrix is low, and the surface layer is easy to peel off and peel under the action of demolding tension, gas expansion force and external forces such as high temperature, shot peening and high pressure.

(3) There are micro pores under the skin, and partial peeling is the result of the release of subcutaneous air shrinkage pores under the action of external force.