Inclusions and shrinkage holes are common defects in the processing of two types of die-cast aluminum. In severe cases, the die-cast aluminum parts will be scrapped. Attention should be paid to and avoided in production.
1. Inclusion
1) Defect characteristics
Inclusions appear on the outside or inside of die-cast aluminum parts. These inclusions are mostly metal oxides, paint residues, etc. Inclusions not only affect the appearance, but also make the internal structure of the casting less dense.
2) Cause
When the metal is melted, it easily reacts with oxygen to form oxides at high temperature; coatings for crucibles that melt the metal: such as zinc oxide, water glass, etc., float on the surface of the liquid metal after shedding; It contains more inclusions. If the above substances enter the mold cavity without being excluded, they will stay in the die-cast aluminum parts and form inclusions.
3) Preventive measures
The metal melting temperature is strictly controlled within the scope of the process regulations, and slag removal should be done as much as possible before pouring, that is, the inclusions floating on the surface of the metal liquid are removed, and the cross-sectional area of the mold exhaust groove is appropriately increased, and the reasonable setting Slag bag.
2. Shrinkage
1) Shrinkage feature
The sparse tissue appears in the die-cast aluminum parts, and some even have a honeycomb shape, which affects the strength of the casting.
2) Cause
After the cavity is filled with liquid metal, it cannot be replenished in a sufficient amount during the shrinking process, and it is likely to occur on castings with uneven thickness. In particular, the injection pressure is too low and the pressure holding time is short, which is more prone to this defect.
3) Preventive measures
The pouring system can be enlarged and opened in the thick part of the die casting. A riser is provided at the shrinkage loosening position to compensate for shrinkage. The structural design of parts should avoid uneven thickness or change to reinforced ribs in thick parts. The process of die-casting aluminum parts is reasonable. If the pouring temperature cannot be too high to prevent large shrinkage, the pressure should be appropriate and the holding time should be sufficient.