Porosity, also known as air hole, is one of the common defects in casting production. It is produced in the interior, surface or near surface of the casting, and it is round, long and irregular in different sizes. There are single or aggregated chips. The hole wall is smooth, white in color, and sometimes covered with a layer of oxide skin. In long-term practice, we generally call them pores, bubbles, pinholes, gas porosity and gas shrinkage pores according to their different shapes and causes.