Improvement on the Service Life of Aluminum Magnesium Alloy Dies (Part One)
As important processing equipment, performance and service life of aluminum magnesium alloy die casting molds have a direct impact on quality of products and economic benefits of the company. The mold material and heat treatment technology are the main factors affecting the service life of aluminum magnesium alloy die casting molds. This article analyzes the main failure modes of aluminum magnesium alloy die casting molds, and briefly introduces typical steel used for molds and common heat treatment methods, pointing out that a reasonable selection of the mold material and heat treatment process can significantly improve thermal stability, hardenability, wear resistance, thermal fatigue and conductivity of molds and improving the service life of the mold.
1. The failure mode of the aluminum magnesium alloy die casting mold
The aluminum magnesium alloy die casting mold is a forming mold used to die-cast aluminum magnesium alloy on a die casting machine. The surface temperature of the cavity can reach about 600 ℃ during operation, and the molten aluminum magnesium alloy liquid is easy to adhere to steel materials. Anti stick coatings should be frequently applied on the mold cavity, which causes severe fluctuations on the surface temperature of the cavity. The failure modes are mainly mold sticking, erosion, thermal fatigue and wear. When the mold cavity structure is complex and there is stress concentration, the mold will also break and fail under the combined action of thermal load and mechanical load.
1.1 Mold sticking
When the aluminum magnesium alloy parts and the mold surface are moving, the partial stress of some contact points exceeds yield strength of the material due to the uneven surface. The sticking point is cut off, making the material on the mold surface transfer to the workpiece or fall.
1.2 Erosion
When the mold surface is in contact with the aluminum magnesium alloy liquid for relative movement, the bubbles formed at the contact part between the liquid and the mold burst to produce instantaneous impact and high temperature, causing the mold surface to form tiny spots and pits. The aluminum magnesium alloy liquid and small solid particles fall at a high speed and repeatedly impact the surface of the mold, causing partial material loss and forming tiny spots and pits on the metal surface. Under repeated action, fatigue cracks will develop on the surface of the die, and even cause partial fractures.
1.3 Thermal fatigue
The surface of the mold is repeatedly subjected to heating and cooling to cause fatigue and form cracks. The main cause for cracks in aluminum magnesium alloy die casting molds is the difference between the pouring temperature and the preheating temperature of the mold. The greater the temperature difference is, the faster the cooling rate becomes and the easier it is for thermal fatigue cracks to occur. Moreover, it is also closely related to the speed of thermal cycles, the heat treatment process and surface treatment of the mold.
1.4 Wear
Because the friction between the mold surface and the processed high temperature magnesium aluminum alloy parts cannot be lubricated, the high temperature workpiece is oxidized. The surface layer of the mold cavity is tempered and softened, and the low hardness increases the wear. The severe wear prevents the mold from processing qualified products.
1.5 Breaking
The phenomenon of large cracks or partial separation of aluminum magnesium alloy die casting molds during operation and loss of normal service capability is called fracture failure. Mold fracture usually manifests partial fragments or the entire mold is broken into several parts.
1. The failure mode of the aluminum magnesium alloy die casting mold
The aluminum magnesium alloy die casting mold is a forming mold used to die-cast aluminum magnesium alloy on a die casting machine. The surface temperature of the cavity can reach about 600 ℃ during operation, and the molten aluminum magnesium alloy liquid is easy to adhere to steel materials. Anti stick coatings should be frequently applied on the mold cavity, which causes severe fluctuations on the surface temperature of the cavity. The failure modes are mainly mold sticking, erosion, thermal fatigue and wear. When the mold cavity structure is complex and there is stress concentration, the mold will also break and fail under the combined action of thermal load and mechanical load.
1.1 Mold sticking
When the aluminum magnesium alloy parts and the mold surface are moving, the partial stress of some contact points exceeds yield strength of the material due to the uneven surface. The sticking point is cut off, making the material on the mold surface transfer to the workpiece or fall.
1.2 Erosion
When the mold surface is in contact with the aluminum magnesium alloy liquid for relative movement, the bubbles formed at the contact part between the liquid and the mold burst to produce instantaneous impact and high temperature, causing the mold surface to form tiny spots and pits. The aluminum magnesium alloy liquid and small solid particles fall at a high speed and repeatedly impact the surface of the mold, causing partial material loss and forming tiny spots and pits on the metal surface. Under repeated action, fatigue cracks will develop on the surface of the die, and even cause partial fractures.
1.3 Thermal fatigue
The surface of the mold is repeatedly subjected to heating and cooling to cause fatigue and form cracks. The main cause for cracks in aluminum magnesium alloy die casting molds is the difference between the pouring temperature and the preheating temperature of the mold. The greater the temperature difference is, the faster the cooling rate becomes and the easier it is for thermal fatigue cracks to occur. Moreover, it is also closely related to the speed of thermal cycles, the heat treatment process and surface treatment of the mold.
1.4 Wear
Because the friction between the mold surface and the processed high temperature magnesium aluminum alloy parts cannot be lubricated, the high temperature workpiece is oxidized. The surface layer of the mold cavity is tempered and softened, and the low hardness increases the wear. The severe wear prevents the mold from processing qualified products.
1.5 Breaking
The phenomenon of large cracks or partial separation of aluminum magnesium alloy die casting molds during operation and loss of normal service capability is called fracture failure. Mold fracture usually manifests partial fragments or the entire mold is broken into several parts.
