Causes of air holes in aluminum alloy die castings:
a. During punching and solidification, the gas evaporated from the coating invades the molten metal, resulting in round holes on the surface or inside of the casting.
b. If the gas content in the alloy liquid is too high, round holes will also be formed during solidification.
Reasons for shrinkage porosity:
a. In the solidification process of liquid alloy, the shrinkage cavity is generated due to the reduction of volume or the final solidification part can not be filled by liquid metal.
b. During heating, due to uneven thickness or local overheating, the casting solidifies slowly in a certain place and shrinks when it is concave with the casting surface.
Due to the existence of pores and shrinkage pores, the surface treatment of die castings is very troublesome. These pores may enter the water. When spraying and baking after electroplating, the gas in the pores will heat and expand, or the water in the pores will become steam, volume expansion and volume expansion. When foaming on the surface of castings, appropriate methods shall be used in production. The reasons for solving these disadvantages.
How to solve the problems of porosity and impurities in aluminum alloy die castings?
Aluminum alloy die casting
1. Hole aluminum alloy die casting:
The key to solve this problem is to reduce the amount of gas added into the casting. In the ideal state, the metal flow state of the alloy should enter the cavity from the nozzle through the sub cone and sprue to form a smooth and uniform metal flow direction. In the study of simulating the die casting process of mold filling system, it can be clearly seen that the rapid change of sprue position and the increase of cross-sectional area will cause the turbulence and entrainment of liquid metal flow. Only when the smooth liquid metal is conducive to the gas entering the overflow groove and exhaust groove from the runner and cavity can it be discharged from the mold. The use of new ceramic filter materials, without the use of twice nozzle materials, also reduces impurities.
2. About shrinkage:
Through reasonable nozzle design, inner gate thickness and position, mold design, mold temperature control and cooling, all parts can dissipate heat as evenly as possible during solidification, solidify at the same time and avoid shrinkage. Pay attention to impurity elements in waste. Control the content of harmful impurities in alloy raw materials, especially the content of lead < 0.002%.