Aluminum alloy die casting porosity causes and Solutions
Aluminum alloy die casting porosity causes and Solutions
Die casting defects, there is the largest pores.
Stomatal characteristics. Have a smooth surface, the shape is circular or oval. The form in the casting surface, or subcutaneous pinhole, and possibly also in casting.
(1) the gas source
1) alloy liquid gas - a related to the raw material
B and melting process
2) casting process in gas around a and die casting process parameters
B and die structure
3) release agent is decomposed to produce gas around a and paint their own characteristics
B and spraying process
(2) raw materials and smelting process to produce gas analysis
In the aluminum liquid gas mainly hydrogen, accounting for about85% of total gas.
The melting temperature is higher, the solubility of hydrogen in molten aluminum is higher and higher, but in solid aluminium solubility is very low, so in the solidification process, the hydrogen evolution pore formation.
The hydrogen source:
1) atmospheric water vapor, liquid metal from humid air absorbing hydrogen.
2) raw material itself, hydrogen content, alloy ingot surface wet, dirty recycled material, oil.
3) tools, moisture flux.
(3) die casting process to produce gas analysis
Due to the pressure chamber, pouring system, the cavity are communicated with the atmosphere, and the metal liquid is high pressure, high speed filling, if not to achieve the orderly, smooth flowing state of liquid metal, vortex, the gas volume.
Die casting process needs to consider the following issues:
1) in the gating system can clean, smooth flow, no separation and vortex.
2) there is no sharp zone or the death zone
3) pouring system whether a cross-sectional area changes?
4) exhaust tank, overflow location is correct? Is big enough? Whether or not it will be stopped? Gas can be effectively, smoothly discharged?
Application of computer simulation of filling process, in order to analyzing the above phenomenon, in order to make judgement to choose the reasonable process parameters.
(4) coating produces gas analysis
Coating properties such as hair: gas porosity has a direct effect on casting.
Spraying process : the use of excessive amount of volatile gas, causing a large amount of lubricant, too much, or burned, is gas source.
(5) solve the blowhole of die casting method
To analyze what causes the pores, back to take corresponding measures.
1) dry, clean alloy material.
2) control the melting temperature, to avoid overheating, degassing treatment.
3) reasonable selection of die casting processing parameters, especially the injection speed. High speed switching point adjustment.
4) sequentially filling in favor of cavity gas discharge, the sprue and runner has sufficient length ( > 50mm ), in order to facilitate the smooth flow of alloy liquid and gas has the opportunity to discharge. Can change the thickness of the gate, the gate, in the formation of pores on the direction of position setting overflow tank, exhaust groove. Relief goods shall not be less than the cross-sectional area of the sum of ingate sectional area60% of the sum, or difference of effect of slag.
5) select the good performance of the coating and spray volume
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