Time:2025-11-26 Browse: 11
With the gradual manifestation of the advantages of aluminum alloy die castings, market demand has continuously urged processing plants to expand production efforts, striving to upgrade and replace existing iron cast products with aluminum alloy or magnesium alloy products as soon as possible. Consequently, processing plants are faced with heavier tasks while having to maintain consistent product quality. Today, we will share methods to prevent some common defects in aluminum alloy die castings.
Characteristics and Inspection Methods: Striped scratches of a certain depth appear on the casting surface along the mold opening direction, which may develop into surface - wide scars in severe cases. Another form occurs when molten metal adheres to the mold, causing scuffing that results in excess material or material shortage on the casting surface.
Causes:
Damage (crushing or impact damage) on the cavity surface.
Excessively small or reverse draft angle in the mold release direction.
Unbalanced ejection, leading to skewed ejection.
Excessively high pouring temperature and mold temperature causing molten alloy adhesion.
Poor performance of the mold release agent.
Iron content in the aluminum alloy is lower than 0.6%.
Rough and uneven cavity surface with low mold hardness.
Preventive Measures:
Repair damaged areas of the mold surface, correct the draft angle, increase mold hardness (HRC 45° - 48°), and improve mold finish.
Adjust ejector pins to ensure balanced ejection.
Replace with a high - performance mold release agent.
Adjust the iron content in the alloy.
Reduce pouring temperature and maintain stable and balanced mold temperature.
Adjust the direction of the ingate to prevent molten metal from directly impacting the core and cavity walls.
II. Blowholes/Porosity
Characteristics and Inspection Methods: Bulges of varying sizes on the casting surface or subsurface cavities.
Causes:
Insufficient filling degree of molten metal in the shot sleeve (should be controlled between 45% - 70%), which easily causes air entrapment, along with excessively high initial injection speed.
Unreasonable mold gating system resulting in poor ventilation.
Excessively high melting temperature, high gas content in the molten metal, and inadequate degassing treatment.
Excessively high mold temperature, insufficient mold holding time, inadequate metal solidification time, and premature mold opening when the casting strength is insufficient, causing trapped gas to expand.
Excessive usage of mold release agent and injection plunger oil.
Too short blowing time after spraying, leaving moisture on the mold surface.
Preventive Measures:
Adjust die casting process parameters, injection speed, and the switching point between low and high injection speeds.
Modify the mold runner and add overflow grooves and vent grooves.
Reduce the mold temperature in defect - prone areas to reduce gas pressure effects.
Optimize the melting process.
Extend mold holding time and adjust the blowing time after spraying.
Control the dosage of mold release agent and injection oil.
III. Cracks
Characteristics and Inspection Methods: Narrow, irregular linear or irregular cracks on the casting surface that tend to propagate under external forces. Cold cracks - no oxidation at the crack edges; Hot cracks - oxidation at the crack edges.
Causes:
Excessively high iron content or excessively low silicon content in the alloy.
High content of harmful impurities in the alloy, reducing its plasticity.
For Al - Si alloys: Excessively high zinc or copper content in Al - Si - Cu alloys; Excessively high magnesium content in Al - Mg alloys.
Excessively low mold temperature.
Sharp changes in casting wall thickness leading to restricted shrinkage.
Overly long mold holding time causing high internal stress.
Uneven force distribution during ejection.
Preventive Measures:
Strictly control the alloy composition; in some cases, add pure aluminum ingots to reduce magnesium content or Al - Si master alloy to increase silicon content.
Improve the casting structure by increasing fillet radii, enlarging draft angles, and minimizing wall thickness differences.
Adjust or add ejection points to ensure uniform ejection force.
Shorten mold opening or core pulling time.
Raise the mold temperature (operating temperature: 180°C - 280°C).
IV. Deformation
Characteristics and Inspection Methods: The geometric shape of the die casting does not conform to the design drawings, which may be overall deformation or local deformation.
Causes:
Poor casting structure design resulting in uneven shrinkage.
Premature mold opening when the casting rigidity is insufficient.
Deformation caused by die sticking/scuffing.
Unreasonable arrangement of ejector pins leading to uneven ejection force.
Improper method for removing the sprue.
Preventive Measures:
Optimize the casting structure.
Adjust the mold opening time.
Reasonably arrange the position and quantity of ejector pins.
Adopt an appropriate sprue removal method.
Eliminate factors causing die sticking/scuffing.
V. Flow Marks and Patterns
Characteristics and Inspection Methods: Visual inspection reveals stripes on the casting surface consistent with the molten metal flow direction, as well as distinct non - directional patterns with a color different from the metal matrix, which do not tend to propagate.
Causes:
Flow marks are left when the first molten metal entering the cavity forms a thin, incomplete metal layer that is later filled by subsequent molten metal.
Excessively low mold temperature.
Undersized or improperly positioned ingate causing molten metal splashing.
Insufficient pressure applied to the molten metal.
Patterns are caused by excessive usage of mold coating and injection oil.
Preventive Measures:
Raise the mold temperature.
Adjust the cross - sectional area or position of the ingate.
Optimize the flow speed and pressure of molten metal in the runner.
Select suitable mold coating and injection oil, and control their dosage.
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