Aluminum Alloy Die casting manufacturers change the mechanical properties of the outer layer by heating and cooling the surface of the mold steel. Surface quenching is the main content of surface heat treatment. Its purpose is to obtain a high hardness mold surface and good internal stress dispersion, thereby improving the wear resistance and fatigue resistance of Aluminum Alloy Die-Casting molds. Aluminum alloy die-casting process for surface heat treatment of metal molds. It is widely used in aluminum alloy die-casting molds, which not only requires high wear resistance, fatigue limit, and large impact load, but also has excellent plasticity and toughness. Surface heat treatment can be divided into surface quenching and chemical heat treatment.
Surface quenching
The mold accessories are heated using different heat sources. When the surface temperature of the Aluminum Alloy Die Casting mold reaches above the critical point (the core temperature of the aluminum alloy die casting mold is below the critical point), the surface of the aluminum alloy die casting mold hardens, and the core maintains its original structure. In order to heat only the surface of the aluminum alloy die casting mold, a high energy density heat source is required. According to different heating methods, surface quenching can be divided into induction heating (high-frequency, high-frequency, power frequency) surface quenching, flame heating surface quenching, electrical contact heating surface quenching, electrolyte heating surface quenching, laser heating surface quenching, electron beam surface quenching, induction heating and flame heating surface quenching have been widely used in aluminum alloy die-casting plants. Chemical heat treatment
The mold accessories are placed in a medium containing active elements for insulation, allowing the active atoms in the medium to penetrate into the surface of the aluminum alloy die-casting mold or produce a covering layer of certain compounds, thereby changing the structure and chemical composition of the mold, and making the aluminum alloy die-casting mold on the surface of the mold have special mechanical or physical and chemical properties. Generally speaking, other appropriate heat treatments should be carried out before and after chemical infiltration to maximize the potential of the infiltration layer and achieve the matching of the structure and properties between the aluminum alloy die casting model core and the mold surface. Chemical heat treatment can be divided into carburizing, nitriding, boronizing, siliconizing, sulfurizing, aluminizing, chromizing, zinc nitriding, carbonitriding, aluminizing, etc
Contact resistance heating quenching
When a voltage of less than 5V is applied to the aluminum alloy die casting mold through the electrode, a large amount of current flows through the contact area between the electrode and the aluminum alloy die casting mold, generating a large amount of resistance heat. It heats the surface of the aluminum alloy die casting mold to the quenching temperature, then takes out the electrode, transfers the heat to the aluminum alloy die casting mold, and rapidly cools the surface to achieve the purpose of quenching.
This method has simple equipment, convenient operation, high degree of automation, small deformation of aluminum alloy die-casting molds, no need for quenching, and can significantly improve the wear resistance and scratch resistance of aluminum alloy die-casting molds, but the hardening layer is relatively thin (0.15-0.35mm). Poor uniformity of microstructure and hardness. Therefore, this method is not widely used in aluminum alloy die-casting plants.
Electrolytic heating quenching
The mold accessories are placed in an electrolyte of acid, alkali, or salt solution, connected to the negative electrode, and the electrolytic cell is connected to the anode. After the direct current is connected, the electrolyte is electrolyzed, oxygen is released on the anode, and radon gas is released on the mold accessories. Hydrogen creates a layer of gas film around the mold parts and becomes a resistor that generates heat. The surface of the mold parts is rapidly heated to the quenching temperature, and then the power is cut off. The gas film quickly disappears, and the electrolyte becomes a quenching medium, causing the surface of the mold parts to rapidly cool and harden. The commonly used electrolyte is a solution containing 5-18% sodium carbonate. The electrolytic heating method is simple, has a short processing time, a heating time of only 5-10 seconds, high productivity, and small quenching deformation. Suitable for small mold parts in aluminum alloy die-casting plants.
Laser heat treatment
The application of laser in heat treatment began in the early 1970s, from the laboratory stage to the production stage. When the surface of the aluminum alloy die-casting mold is covered with 40; 10wcm&41; When high-energy density focused laser irradiation is applied, the surface of the die-casting die rises to the quenching temperature within a fraction of a second or even a thousandth of a second. Due to the rapid heating of the irradiation point, heat cannot be transferred to the surrounding metal in a timely manner. Therefore, when the laser stops shooting directly, the metal around the bright spot will act as a quenching medium, absorbing a large amount of heat, allowing the bright spot to cool quickly and achieve a very precise arrangement and high mechanical properties. If the surface is heated to a sufficiently high wetting temperature, the metal surface can receive sufficient wetting. This operation is called polishing.
Laser heating can also be used for local alloying treatment, that is, coating a layer of wear-resistant or heat-resistant metal on the metal surface, or laser heating can also be used for local alloying treatment, that is, in aluminum alloy die-casting molds that are prone to damage or need to be heat-resistant, or coating wear-resistant or heat-resistant metal on the coating, and then rapidly melting through laser irradiation to produce wear-resistant or heat-resistant alloy layers. In order to ensure the service life and heat resistance of the workpiece, a layer of chromium is plated on the parts that require heat resistance, and then rapidly melted by laser to produce a hard and heat-resistant surface layer containing chromium.
The electron beam heat treatment technology of Zinc Alloy Die-casting manufacturers has been studied and applied since the 1970s, and can be used for the initial continuous annealing of thin steel strips and wires. The energy density can reach 10wcm. Electron beam surface quenching has the same characteristics as laser, except that it needs to be carried out in vacuum. When the electron beam bombards the metal surface, the impact point rapidly heats up. The penetration depth of an electron beam depends on the acceleration voltage and data density. When the electron beam bombards the surface in a short period of time and the substrate remains hot, the surface temperature rapidly increases. When the electron beam stops igniting, heat quickly transfers to the cold base material, causing the heated surface to self harden. In order to effectively perform self cooling quenching, the ratio of the volume of the entire mold part to the volume of the quenched surface should be maintained at least 5:1. The depth and time of bombardment are related to the surface quenching temperature. The heating speed of electron beam heat treatment is fast, and the austenitization time is only a few seconds or even shorter. Therefore, the surface grain size of the workpiece is very small, the hardness is higher than that of general heat treatment, and it has excellent mechanical properties, which improves the efficiency of aluminum alloy die-casting plants.
