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2020.10.28
Aluminum alloy die casting process is a kind of production process which pays attention to skills. There are many kinds of situations that may occur. We can’t predict accurately so as to avoid these phenomena. We can only take measures to solve these problems in time after discovery. In addition to the blackening phenomenon caused by high pH value of cutting fluid in aluminum die casting, white spots often appear on the processed products. So, if there are large and small white spots after aluminum alloy die casting processing, what should we do? In this article, we will analyze the causes to white spots after aluminum die casting anodizing and solutions & how to deal with the white spot problem after aluminum alloy die casting process.
In general, white spots appear at the joint between the inner gate and the casting, the joint of the runner in the gating system, the upper part of the sprue and the gate cup. There are several reasons for white spots:
1. Improper operation, improper handling of the connection between the runner and the casting, the connection of the runner in the gating system, the sprue and the gate cup, resulting in incomplete bonding.
2. Coating layer, because of the uneven thickness of the surface coating layer, and under the strong suction of the vacuum pump, the sand leakage at the crack.
3. If the quality of the binder is poor, especially the high-temperature adhesive force is not enough, it will lead to differentiation and decomposition, sand leakage at the bonding place, etc. sand particles will adhere to the casting surface under high temperature baking, and in serious cases, sand scaling may occur.
4. There are too many pores in the surface structure of aluminum alloy die castings, which are caused by too much porosity.
5. If there are too many impurities in the raw materials, there will be many white spots in the aluminum alloy die casting.
● High voltage and high current density impact method. In the early stage of anodizing, high voltage and high current impulse are used to connect the “island” which were originally separated by impurities into pieces by high current impulse. After cleaning, the oxide film can be dyed satisfactorily, and the white spots almost disappear.
● Surface grinding of casting. Grinding can make the milled aluminum powder fill the pores of the casting and act as a bridge connecting the blocks isolated by impurities. Because the polished aluminum powder sometimes can not play a real role in filling and bridging, some parts of the filler will be corroded and fall off in the process of alkali corrosion and anodic oxidation.
● Shot peening on casting surface. Before the shot peening method was tried, use the round head hammer to knock. The reason is that the gap blocking the “island” can be closed by knocking to achieve the purpose of connecting into pieces. The result is remarkable.
In the production of aluminum die casting, the auxiliary bottom aluminum should not be splashed, and the aluminum temperature should be properly raised. The prevention of white spot can not only avoid cracks to a certain extent, but also prolong the life of aluminum die castings.
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