I. Characteristics
(1) The surface of the casting has linear or wavy lines, narrow and long, with development trend under external force;
(2) Cold fissure-cracking where the metal is not oxidized;
(3) Hot fissure-cracking where the metal has been oxidized.
II. Causes
(1) Excessive iron content or silicon content in the alloy;
(2) The content of harmful impurities is too high, which reduces the plasticity of the alloy;
(3) Aluminum-silicon-copper alloy contains too much zinc or too little copper;
(4) The overall temperature of the mold, especially the mold cavity, is too low;
(5) casting wall thickness, thin storage of drastic changes in the place of contraction is blocked, the sharp corners of the formation of stress;
(6) Stay in the mold for too long, stress;
(7) Uneven force during ejection.
III. Treatment Methods
(1) correctly control the alloy composition, in some cases can be added to the alloy of pure aluminum ingots to reduce the amount of magnesium in the alloy or aluminum alloy with aluminum brick intermediate alloy to improve the silicon content;
(2) Change the casting structure, add angle, change the slope of the mold, reduce the wall thickness difference;
(3) Change or increase the ejection position, so that the ejection force is uniform;
(4) Shorten the mold opening and core extraction time to improve the mold temperature, to maintain the thermal balance of the mold.
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