Aluminum alloy die-casting defects - oxidation slag inclusion reasons:

The charge is not clean, and the amount of returned charge is too much

Poorly designed gating system

The slag in the alloy liquid is not cleaned up

Improper pouring operation, bringing in slag inclusions

Insufficient standing time after refining and metamorphism

Through the analysis of the scrap parts of aluminum alloy die-casting, there are three main forms of slag inclusion in the gate: shrinkage cavity, oil pollution and chilled layer. Among them, oil stains are mostly slag inclusions, accounting for more than 60% of the total slag inclusions; chilled layers account for about 35% of the total slag inclusions; and shrinkage cavities account for 5% of the total slag inclusions.

1. Similar shrinkage defects

When the sprue cake of the aluminum alloy die-casting part is knocked off, there are irregularly shaped, relatively clean inside and rough surface-like holes at the gate. The gate surface of aluminum alloy die-casting parts with slag inclusions such as shrinkage holes is concave, and the appearance is still not smooth after grinding and painting. The reason is that the temperature of the inner gate is relatively high (the measured maximum mold temperature is 380 ℃), which is the last solidified part, which causes the Al liquid to be too late to be fed, resulting in shrinkage defects.

2. Oil pollution defects

 

The punch needs to be filled with lubricating oil for each casting cycle. The punch oil is not completely burned after the Al liquid is poured, and is wrapped in the Al liquid to form impurities and fill the cavity together. Because the Al liquid coated with punch oil has a lower temperature, it solidifies earlier and flows slowly, so it stays at the end of the product at the end of filling. In addition, the cross-sectional area of ​​the ingate is small and the flow resistance is large. This part of the Al liquid impurity, which is wrapped with punch oil and solidified in advance, is more difficult to pass through and stagnates near the ingate. After knocking off the material cake, black holes appear at the inner gate with rough inner walls and obvious oil stains on the surface. Check the gate and cake for slag inclusions, and also find such impurities. When the sprue cake of the aluminum alloy die-casting part is knocked off, there are irregularly shaped, relatively clean inside and rough surface-like holes at the gate. The gate surface of aluminum alloy die-casting parts with slag inclusions such as shrinkage holes is concave, and the appearance is still not smooth after grinding and painting. The reason is that the temperature of the inner gate is relatively high (the measured maximum mold temperature is 380 ℃), which is the last solidified part, which causes the Al liquid to be too late to be fed, resulting in shrinkage defects.

3. Chilled layer defects

The chilled layer refers to the shell formed by the rapid condensation of the Al liquid injected into the barrel and the low-temperature surface of the barrel (the chemical composition of the chilled layer was checked by the spectrometer and found no abnormality, all within the standard allowable range). It is filled into the cavity together with the Al liquid. The density of the solid chilled layer (2.7g/cm²) is larger than that of the liquid (2.45g/cm²) Al liquid. During the low-speed operation of the punch, the chilled layer slowly gathers at the end of the Al liquid. When the punch runs at high speed, part of the chilled layer will be drawn into the cavity and form defects. The final form of chilled layer that remains in the gate. The chilled layer is mostly flake-like, the surface is shiny and hard, and there are many gaps with the surrounding base metal, which not only affects the appearance, but also reduces the strength of the aluminum alloy die casting.

Summarize the shortcomings of the existing production conditions and the correlation with the slag inclusion, so as to formulate corresponding improvement measures to ensure the appropriate mold temperature, correct the wrong way of punch lubricating oil supply, realize the standardization of aluminum alloy smelting, and verify the effect, so that the Slag inclusion problem is effectively controlled