The second is the surface grinding method of aluminum casting. Grinding can make the milled aluminum powder fill the pores of the casting, and play the role of connecting the "islands" isolated by impurities.
The third method is shot peening on the surface of aluminum casting. Before the trial of shot peening, the author used the method of hammering with a round head. The original intention was to make the gap between the "islands" closed by hammering, so as to achieve the purpose of connecting into a piece, and the effect was remarkable.