The Detail Analysis Of Aluminum Die Casting Mould Crack Failure

The crack failure of aluminum alloy die-casting mode will not only affect the mold production quality and production efficiency, but also increase the production cost. In reality, the reasons for the cracking and failure of aluminum alloy die-casting molds are diverse. For example, liquid metal has repeated impacts on it, production conditions are hot-corrosive, mold production materials, and EDM and other reasons. In this paper, a special analysis of the cracking failure of aluminum alloy die-casting die is carried out. It is hoped that it can play a role in attracting new ideas, and bring reference value to relevant workers.

The working conditions of aluminum alloy die-casting molds are compatible with high temperature and high pressure. At the same time, the aluminum alloy die-casting mold in working mode needs to withstand the repeated impact of liquid metal. In actual production, due to the high cost of aluminum alloy die-casting molds, long production cycle, and premature failure, the service life will be greatly shortened. -Once the problem of cracking and failure of aluminum alloy die-casting molds is not effectively solved, it will directly affect the economic benefits of the production enterprise. For this reason, more and more aluminum alloy die-casting manufacturers have increased their crack failure analysis. The following content takes H13 steel hot work die steel as an example, and combines the actual production process to analyze the causes of cracking and failure of aluminum alloy die-casting molds from the aspects of aluminum alloy mold material, microstructure and electric discharge machining. Corresponding measures have been taken.

1. Cause Analysis Of Aluminum Alloy Die-Casting Mould Cracking Failure 

Chemical Composition

From the point of view of chemical composition, H13 steel type hot work die steel mainly covers the concentrated elements of C, SijMn, Mo, Cr, and V. From the point of view of chemical characteristics, H13 steel type hot work die steel belongs to low Si and high Mo hot work die steel in terms of material. In the production process, manufacturers will appropriately reduce the Si content or increase the Mo content in the steel according to actual needs. By reducing the Si content, the bias can be effectively reduced

The occurrence of precipitation phenomenon, and further refine the austenite grains, improve the strength and toughness of steel. Increasing the content of Mo can improve the hardenability, tempering resistance and heat resistance of steel. And effectively prevent the precipitation of grain boundary carbides in the steel, as well as the transformation of bainite. Practice has shown that low Si and high Mo steel will reduce the probability of undercooling during the solidification process, thereby effectively preventing the occurrence of dendrites, cellular columnar crystals and dendrite segregation. The combination of Mo and V elements can form alloy carbides, such as VC, MoC and Mo2C. Alloy carbides will precipitate in a finely dispersed state under suitable high temperature conditions, which will greatly improve the thermosetting properties of high temperature materials. Although in terms of chemical composition, H13 steel type hot work die steel has strong crack resistance, in actual operation, we found that H13 steel type hot work die steel has early cracking failure. In order to better analyze the causes of crack failure, it is necessary to effectively combine the microstructure of H13 steel hot work die steel for further analysis.

Microstructure

In order to comprehensively study the microstructure of aluminum alloy die-casting molds, this part uses mold materials that have not been put into use after vacuum quenching and tempering and used mold materials as the research objects to analyze the microstructure of aluminum alloy die-casting molds, and then find out Causes of cracking failure.

Mold Materials That Have Not Been Put Into Use After Vacuum Quenching And Tempering

Through practice, it is found that there are uneven tissues distributed on the substrate of the research object after heat treatment. By observing the research object under a low-power microscope, we found that a large number of precipitated granular carbides are distributed on the matrix and segregated. In other words, compared with the carbides of normal tissues, this part of the carbides Larger in volume. Due to the excessive precipitation of carbides and alloy carbides, the mold material loses a large amount of surrounding carbon and alloying elements. Under normal circumstances, the segregated carbides of the mold will not easily dissolve when the mold is heated by quenching. However, due to its lack of carbon and alloying elements, it is easy to change to martensite under high temperature heating, thereby reducing Tempering the quality star, and greatly reduces the strength and toughness of the steel, making it easy to fracture just now. By using a low power microscope to observe the annealed steel before vacuum quenching, we found that the steel matrix also has segregation. The appearance of this phenomenon means the lack of uniformity of steel raw materials. And once the segregation phenomenon is not effectively dealt with, it will increase the risk of mold cracking and failure, and affect the final service life of the mold.

Mold Material After Use

In actual production, general H13 steel hot work die steel molds will appear to different degrees of cracking on the surface of the mold after about 30,000 times of use, such as: intergranular fractures and the intersection of multiple cracks After peeling, pits and the like are formed. The reason for this phenomenon is mostly due to metallurgical defects in the raw materials.

EDM

EDM is one of the commonly used processing methods in aluminum alloy die-casting molds. Compared with other processing methods, this processing method presents the advantages of high processing accuracy, high level of automation and ease of processing irregular-shaped parts in the specific application process. Nevertheless, the sparks released during processing have the characteristics of high temperature and high pressure, and the temperature of the working fluid will be

The sharp decline has caused the steel surface to be divided into thermal remelting zone and heat-affected zone. The so-called thermoremelting zone means that the surface metal is melted by the high temperature released during discharge. Because the melt is not completely thrown out, and the retained melt solidifies as the working fluid cools. The thermal remelting zone is mostly distributed on the uppermost layer of the steel surface. Compared with the heat-affected layer in the thermal remelting zone, the metal material is affected

After being burned at high temperature, no melting phenomenon occurred, but the metallographic structure of the material changed accordingly. Through a lot of practice, we found that the hot mold process will also increase the risk of mold cracking and failure in the hot remelting zone and the heat affected zone. After the aluminum alloy die-casting mold after EDM passes through the gas furnace, although the metallographic structure of the mold does not change accordingly, it is thermally remelted.

However, slight cracks will appear in the zone, and when the cracks extend to the heat-affected zone, the micro-crack range will increase again, which in turn increases the degree of mold cracking failure.

2.Preventive Measures Against Cracking Failure Of Aluminum Alloy Die-Casting Mold

• 2.1 Increasing the number of samples for metallographic testing of raw materials for aluminum alloy die-casting molds In the actual production process, many manufacturers have not fully conducted metallographic testing of the purchased raw materials in order to speed up the production schedule. In order to reduce the occurrence of cracks and failures of aluminum alloy die-casting molds, manufacturers need to increase the number of metallographic inspections of raw material samples in the annealed and vacuum quenched and tempered states, so as to ensure that the mold materials meet the actual production needs to the greatest extent. When extracting mold material samples, the producer needs to choose the sampling location scientifically and reasonably. In the sampling of aluminum alloy die-casting molds, in order to ensure the integrity of the default core part and detect the accurate quality of mold raw materials, producers generally use the gate as the sampling location.
• 2.2 Effectively solve the thermal remelting zone caused by EDM:The thermal remelting zone caused by electrical discharge machining has higher hardness and greater brittleness, and microcracks are prone to appear during the machining process. Especially in the flame roasting process, the probability of micro-cracks is greater. In order to avoid cracks and failures of aluminum alloy die-casting molds, it is necessary to scientifically and reasonably avoid the appearance of hot remelting zone. After EDM, the hot remelting zone needs to be removed in time, and the mold should be tempered in time to greatly eliminate the residual stress of the affected layer. .
• 2.3 Effectively avoid the phenomenon of early cracking failure:The cracking failure of aluminum alloy die-casting molds occurs in the early stage, which is mostly caused by the excessively high forging temperature of the blank forging. The cracking failure caused by this reason is an irremediable defect. Therefore, in the process of blank production, the producer needs to strictly control the forging temperature. In the quenching heating stage, it is also necessary to arrange the heating time scientifically and reasonably to effectively control the heating temperature and prevent the occurrence of decarburization. In the quenching and cooling stage, it is necessary to effectively control the cooling time, and strive to complete the quenching and cooling process in the shortest time and at the fastest speed. For the cooling water channel, the designer needs to keep the distance between it and the profile and corners large enough to ensure the smooth progress of the cooling process.
• 2.4 Scientific and reasonable heat treatment of the mold:The quality of raw materials for die-casting molds affects the service life of aluminum alloy die-casting molds to a large extent. Therefore, the staff needs to choose the appropriate die-casting mold raw materials based on the actual needs. After the workman determines the raw materials for aluminum alloy die-casting molds, it is necessary to conduct heat treatment in time. At the same time, it is necessary to do a good job in the stress relief process in the production stage to prevent stress concentration, and to control the R angle.System work. -Generally, when the aluminum alloy die-casting mold is used for about 10,000 times, it needs to be tempered in time to remove the stress, so as to effectively prevent the stress concentration from causing the mold to crack and fail. In order to increase the use time of the mold as a whole, multiple tempering and stress relief methods can be used.
• 2.5 Scientifically and reasonably control the temperature in the production process of aluminum alloy die-casting molds:The production process of aluminum alloy die-casting molds presents high temperature and high pressure. Therefore, it is particularly important to scientifically and reasonably control the temperature in the production process. In the production process, the producer can use a suitable thermometer to calculate the maximum temperature in the die-casting process and take effective control measures to control the temperature within 650 degrees.

3. Conclusion

In short, with the rapid development of my country's social economy, aluminum alloy die-casting mold manufacturers have rapidly expanded in terms of number and production scale. However, due to the large investment in the production cost of aluminum alloy die-casting molds, once the production quality cannot be effectively guaranteed, it will directly affect the production efficiency and market competitiveness of the manufacturer. In the production process, crack failure is a common quality problem of aluminum alloy die-casting molds. This has not only attracted extensive attention from manufacturers, but has also been widely used to affect consumers. For this reason, it is particularly important to increase research on crack failure of aluminum alloy die-casting molds. The above content analyzes the causes of crack failure of aluminum alloy die-casting molds, and proposes preventive measures against cracking failure of aluminum alloy die-casting molds on this basis. It is hoped that it can bring certain reference value to relevant workers and promote the sustainable, rapid and healthy development of my country's aluminum alloy die-casting mold industry.

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