Cause Analysis of Defects in Aluminum Alloy Die Castings

Analyze aluminum die casting defects-the cause of oxidation and slag inclusion:

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

Poor gating system design

The slag in the alloy liquid is not cleaned

Improper pouring operation brings in slag

Not enough standing time after refining and deterioration treatment

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

1. Similar to shrinkage defects

After knocking off the runner cake of aluminum alloy die-casting parts, the irregular shape, relatively clean inside and rough surface similar to shrinkage-like holes appeared at the gate. The gate surface of the aluminum alloy die casting with shrinkage cavity and slag inclusion is sunken, and the appearance is still not smooth after polishing and coating. The reason is that the temperature of the inner gate is relatively high, which is the place where the final solidification occurs, causing the Al liquid to be too late to feed and shrinkage defects.

2. Oily defects

Each casting cycle needs to add lubricating oil to the punch. 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 temperature of the Al liquid wrapped with punch oil is lower, it will solidify earlier and flow at a slower speed, so it stays at the end of the product at the end of filling.

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 spectrometer checks the chemical composition of the chilled layer and no abnormalities are found, all within the standard allowable range). It is filled into the cavity along with Al liquid. The density of the solid chilled layer is greater than that of the liquid Al liquid. During the low-speed operation stage 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.

Summarize the shortcomings of the existing production conditions and the relevance to slag inclusion, so as to formulate corresponding improvement measures to ensure the appropriate mold temperature, correct the wrong punch lubricant supply method, realize the standardization of aluminum alloy melting, and verify the effect, so that The slag inclusion problem is effectively controlled.

 

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