Reasons for blistering in zinc alloy die-casting:
1. Caused by holes: mainly pores and shrinkage mechanism. The pores are usually round, but most constrictions are irregular. (1) Cause of pores: During the inflation and solidification process, due to gas intrusion, the metal liquid produces pores on the surface or inside the casting. BThe gas evaporated from the paint invades. c The gas content of the alloy liquid is too high, causing coagulation and precipitation. When the mold is poorly vented, the gas in the cavity and the volatile gases from the paint will remain in the casting to form pores. (2) Reasons for shrinkage: During the solidification process of liquid metal, due to volume reduction or the final solidified part is not a liquid metal material and shrinks holes. B The uneven thickness of the casting or the casting is locally overheated, causing the surface to solidify slowly during volume shrinkage, forming a concave surface. Due to the existence of pores and shrinkage holes, water can enter the surface of the die casting. When painting and electroplating, the gas in the hole thermally expands, or the water in the hole turns into steam and expands in volume, resulting in bubbles on the surface of the casting.
2. Intergranular corrosion of harmful impurities in zinc alloys: Lead, cadmium, and tin will gather at the crystal boundary, leading to intergranular corrosion, intergranular corrosion, and breakage of the metal substrate and coating, accelerating disaster, and intergranular corrosion in this area will expand. top, causing bubbles on the surface of the casting. Especially in humid environments, intergranular corrosion can cause castings to deform, crack, or even break.
3. Causes of cracks: water, cold partition lines, thermal cracks. 1) Water and cold cutoff line: During the charging process of the metal liquid, the metal liquid enters the contact wall and solidifies prematurely, and then the liquid metal and metal solidification can be integrated, and strip defects appear in the form of joints on the surface of the casting. Water is usually shallow on the surface of the casting and the cold barrier may penetrate into the casting. 2) Thermal cracks: When the wall thickness of the casting is uneven, stress produces a solidification process; B. premature ejection, insufficient metal strength; C. high mold temperature, uneven ejection force, and coarse grains; E. the presence of harmful impurities. These parameters can be hacked. When the die casting has water marks, cold cracks, hot cracks and plating solution, the cracks will penetrate and convert into steam baking, and the metal will be deposited on the top of the pressure to form blisters.
Methods to solve zinc alloy die-casting defects:
1. Control of pore generation: The key is to reduce the amount of casting mixture. The ideal metal flow should continuously accelerate the nozzle into the mold cavity through the diverter cone and pouring channel to form a smooth metal flow direction. This purpose is achieved by adopting a tapered flow channel design, that is, the pouring flow should continuously accelerate and gradually decrease from the nozzle to the pouring opening. In a filled system, the mixed gas forms pores due to the mixing of turbulent flow and metallic liquid. The liquid metal entering the mold cavity during the simulated die-casting process significantly increases the changes in the pouring port of the flow channel, causing turbulence and gas entrainment in the flow of metal liquid. The liquid metal is smooth, which is conducive to the gas entering the overflow groove from the pouring port and cavity. and exhaust slots.
2. Shrinkage: Make all parts of the zinc alloy die-cast casting as far away as possible while dissipating heat and solidifying evenly. Avoid shrinkage through proper nozzle design, mold design, gate thickness and location, mold temperature control and cooling. Intergranular corrosion: Control the main impurity content of harmful alloy materials, especially lead 0.003%. Watch out for waste and impurities.
3. Water and cold barrier: It can increase the mold temperature, increase the internal gate speed, or add an overflow groove in the cold barrier area to reduce the cold appearance of closed grain.
4. Hot cracks: The thickness of zinc alloy die castings does not change quickly, reducing the generation of stress; die casting process parameters and adjustments; reduce mold temperature