Aluminum alloys play an important role in modern manufacturing industry. The main reasons are as follows:
(1) Die castings with high dimensional accuracy and good surface quality.
(2) High material utilization.
(3) The die castings with complex shape, clear profile, deep cavity and thin wall can be produced.
(4) The die castings are denser and have higher strength and hardness.
(5) The production efficiency is high, and it is easy to realize mechanization and automatic production.
(6) The economic benefit is good, and the parts of the other materials can be directly inlaid on the die casting parts, which saves the valuable materials. In particular, the automobile industry has already adopted a large number of aluminum alloy parts made to reduce weight and energy saving.
Die casting molds play an extremely important role in aluminum alloy molding. The melting temperature of aluminum is 680℃, and because of the high temperature during die casting and the high pressure during filling, the life of aluminum die casting die is very low. According to statistics, the common failure modes of die casting molds are chap, cracking, erosion, adhesion and deformation.
During the cycle of each die casting, due to the intense heat exchange, the temperature of the mold changes sharply, and the thermal stress produced by it causes thermal fatigue on the surface of the mold cavity and forms the micro crack. With the increase of the times of die casting cycles, the micro cracks expand further and form chap. This is the main form of aluminum alloy die casting failure.
In die-casting production, in addition to thermal stress, other stresses are also generated inside the mold due to the high-pressure impact of the aluminum liquid. When the stress exceeds the fatigue limit of the mold material, the crack is produced, especially the sharp corner of the stress concentration, which is more likely to crack. If the stress produced in the die processing is not completely eliminated, the die is easier to crack.
The frictional heat generated during the high-speed filling of the cavity by the aluminum liquid causes the surface temperature of the surface of the mold cavity facing the inner runner to be high. With the heavy impact of aluminum liquid, the surface protection layer of the site is easily destroyed, and the aluminum liquid is further reacted with the exposed metal matrix to produce hard compounds. In the process of removing these compounds, it is easy to take away the substrate material, so the cycle will aggravate the damage of the cavity surface and cause serious erosion.
During the cavity filling of aluminum alloy, the instantaneous temperature of the cavity surface is above 600℃. At this time, the affinity of the die material and the aluminum liquid is strong and the adhesion is strong.
In the process of die casting, the die casting mould is subjected to a variety of stresses, such as clamping force and anti pressure. If the rigidity of the template is not enough, the die will produce bending deformation under the long-term action of these stresses.