Crack Tendency And Stress Generation Of Aluminum Alloy
|During the solidification and shrinkage of the alloy, the external resistance is too large, and it is easy to generate cracks. Aluminum die-casting generally has a tendency to crack, while Al-Si and Al-Mg alloys have a higher tendency to crack.|
The cracks are different from hot cracks and cold cracks. Observe the cracks, the appearance is zigzag and irregular, the surface is strongly oxidized, the matte is hot cracks, and the head is cold cracks.
Hot cracking occurs during the solidification of the alloy, that is, most alloys have formed a dendrite skeleton and began to solidify, but there is still a small amount of liquid in the dendrite parts. At this time, the linear shrinkage of the alloy is the largest and the thermal strength of the alloy is very low. The mold hinders its shrinkage and generates shrinkage pressure. When its strain is greater than the allowable strain of the alloy’s strength at this temperature, cracks occur.
Cold cracking is that the alloy is severely hindered or subject to external forces when the solid is shrinking, such as premature falling sand or mechanical damage during cleaning. Cold cracking rarely occurs.
When the casting is blocked during the solidification and cooling process in the mold, stress and deformation will occur. The stress is in the range of elastic strength. Residual stress will exist in the casting, reducing the design strength of the casting. The casting will deform during use and processing, affecting the precision and assembly of the casting. .
Casting stress consists of three parts: thermal stress, phase transformation stress and shrinkage stress. The casting stress of die castings can be eliminated by annealing the natural failure of the goods.
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