Replacing traditional steel with aluminum alloy to make cars can reduce the weight of the whole car by about 30%. Because the die-casting mold is a high-pressure (30 ~ 150MPa) 400 ~ 1,6000C molten metal die-casting molding. During the molding process, the mold is periodically heated and cooled, and is eroded and corroded by hot metal sprayed at high speed. The mold materials require higher thermal fatigue resistance, thermal conductivity, good wear resistance, corrosion resistance, and high temperature mechanical properties. To meet the ever-increasing performance requirements, it is still difficult to satisfy the application of mold materials alone. Various surface treatment technologies must be applied to the surface treatment of die casting molds to meet the requirements of high efficiency, high precision and long life of die casting molds.
Change the surface chemical composition to strengthen
(1) Carburizing.
Carburizing is a surface chemical heat treatment process that places steel in a carburizing medium and heats it to a single-phase austenite zone for a certain period of time to allow carbon atoms to penetrate the steel surface. Carburization is performed above At3 (850 ° C to 950 ° C). Its purpose is to increase the carbon concentration of the surface of the mold after heat treatment, so that the hardness, wear resistance and contact fatigue strength of the surface layer are greatly improved compared with the core, while the core maintains a certain strength and high toughness. There are solid carburizing and liquid carburizing.
(2) Nitriding.
Nitriding is a chemical heat treatment that allows active nitrogen atoms to penetrate the workpiece surface at a certain temperature. Its purpose is to improve the surface hardness, wear resistance, fatigue limit, thermal hardness and seizure resistance of the workpiece. Generally, after quenching and tempering (45-47HRC), the die-casting mold must be nitrided, and the depth of the nitrided layer should be 0.15-0.2mm. There are gas nitriding, ion nitriding. H13 steel is used as the hollow die of extruded aluminum profile, oil quenched at 1,80 ° C + 560%: twice tempered x2h, hardness 48HRC. After ion nitriding at 520 ℃ x4h, the profile extruded from the mold was increased from 1,000kg to 4,500kg, and the service life was increased by 3 times.
Optimize mold design and die casting process
Reduce sharp corners and corners on the mold, use materials reasonably, and standardize processing and heat treatment processes. The nitriding treatment of the mold should control the surface hardness of the mold HV,> 600, and the depth of the nitride layer reaches 0.12 ~ 0.2mm. Preheat the mold correctly, optimize the mold to improve the internal cooling, make the mold obtain a uniform heat balance effect, make the mold maintain a stable and low temperature, spray the coating reasonably, the coating is important for delaying thermal fatigue cracks, and improve the mold life and benefit .
