The reason of the defect oxidation slag inclusion in Shandong Aluminum alloy die casting is as follows
The charge is not clean and the amount of returned charge is too much
Poor gating system design
The slag in the alloy liquid is not cleaned up
Improper pouring operation leads to slag inclusion
The standing time after refining modification is not enough
According to the analysis of scrap parts of aluminum alloy die casting, there are three main forms of slag inclusion in gate: shrinkage cavity, oil stain and cold hard layer. Among them, the amount of oily sludge is the most, accounting for more than 60% of the total amount of slag; The cold hard layer accounts for about 35% of the total slag inclusions; The shrinkage cavity accounts for 5% of the total slag.
1. Similar shrinkage defects
When the runner cake of aluminum alloy die casting is knocked out, the shrinkage like holes with irregular shape, clean interior and rough surface appear at the gate. The gate surface of aluminum alloy die casting with shrinkage cavity and slag inclusion is concave, and the appearance is not smooth after grinding and coating. The reason is that the temperature of the inner gate is relatively high (the measured high mold temperature is 380 ℃), which is the subsequent solidification position, resulting in the lack of time for Al liquid feeding, resulting in shrinkage defects.
2. Oil pollution defects
Each casting cycle needs to add lubricating oil to the punch. The punch oil does not burn completely after pouring in the Al liquid, and is wrapped in the Al liquid to form impurities and fill the mold cavity together. Because of the low temperature of Al liquid coated with punch oil, it will solidify earlier and flow slowly, so it will stay 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, which makes it difficult for the Al liquid impurities wrapped with punch oil and solidified in advance to pass through and stagnate near the ingate. After knocking out the cake, there are black holes in the inner gate, with rough inner wall and obvious oil stains on the surface. This kind of impurity was also found by checking the slag inclusion in the gate and cake.
The cold hard layer refers to the shell formed by the rapid condensation of the liquid Al injected into the barrel and the low temperature surface of the barrel (no abnormality is found in the chemical composition of the cold hard layer by the spectrometer, which is within the allowable range of the standard). It is filled into the cavity together with the liquid Al during the high-speed filling. The density of cold hard layer in solid state (2.7g / cm?) Specific liquid (2.45G / cm?) During the low speed operation of the punch, the cold and hard layer slowly accumulates at the end of the liquid al. When the punch runs at high speed, part of the cold hard layer will be drawn into the cavity, forming defects. Finally, the morphology of the cold and hard layer in the inner gate remains. The cold hardening layer is mostly thin sheet, with glossy and hard surface, and there are many gaps with the surrounding base metal, which not only affect the appearance, but also reduce the strength of aluminum alloy die casting.
This paper summarizes the deficiency of existing production conditions and the relevance with slag inclusion, so as to formulate corresponding improvement measures, ensure the appropriate mold temperature, correct the wrong punch lubricating oil supply mode, realize the standardization of aluminum alloy smelting, verify the effect, and effectively control the slag inclusion problem.
Methods to prevent oxidation slag inclusion:
1. Pouring liquid metal from riser to improve riser design
2. The furnace charge shall be clean without corrosion
3. Riser is set at the shrinkage porosity of casting, and chill is placed or combined with riser
4. Control the moisture of molding sand and dry the sand core
5. Take measures to refine the grain size
6. Improve the position of the casting in the mold and reduce the pouring temperature and pouring speed