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Abstract: This paper mainly introduces the composition data and metallographic diagram of Zamak12 zinc alloy ingot when the aluminum content is low or high; The influence of segregation on the production process and product performance of die casting products, the difficulty of die casting blank defects and countermeasures.

Key words: melting ingot composition segregation metallographic die casting blank difficult defects die performance

Under the background of severe social and economic situation, the production requirements of precision, lightweight, energy-saving and green die-casting processing products have been continuously strengthened, which is the improvement of human awareness of environmental and energy protection and conservation; The application of raw materials in products is constantly expanding green and energy-saving. Under this trend, aluminum based zinc alloy die-casting products in the hardware industry have great advantages. They have high strength, creep resistance and good damping properties. In particular, Zamak12 shows considerable advantages among high aluminum based zinc alloy products. Among zinc alloys, Zamak8 is the only material that can be used for rapid die casting of hot chambers.

Zamak12 zinc alloy raw material has both high quality and weak points. As the content of aluminum in the executive standard is 10.8~11.5%, aluminum segregation is relatively serious in the ingot production of raw materials. The range of aluminum segregation is greatly different in the production of small tonnage smelting furnace and large tonnage smelting furnace; According to the trial production conclusion, the large tonnage furnace is not suitable for the production of Zamak12 raw materials. Due to the large capacity, the heat preservation and discharge time are too long, the aluminum easily floats up, and the composition segregation in front of the furnace and at the furnace bottom is large. That is to say, the small tonnage smelting furnace is more suitable for smelting Zamak12 high aluminum zinc alloy because of the small amount of alloy solution, short discharge time, and small upper and lower segregation of aluminum composition furnace; The element composition and metallographic diagram of the alloy in the ingot are used to analyze the influence of raw material structure and segregation on the die casting process.

1、 Microstructure comparison of Zamak3 and Zamak12 zinc alloys:

Figure 1 Zamak12 Figure 2 Zamak3

1) From the comparative observation of metallographic diagrams Zamak12 and Zamak3, the leaf shape figure 2 of the material structure is much thinner and thicker than that of figure 1, and the crystal group

Figure 1 is much more delicate than Figure 2; It can be seen that the higher the aluminum content, the more delicate the crystal structure will be, and the aluminum content will be less

The grains of natural Al Zn phase are sparsely distributed in the alloy structure, that is, the metallographic structure Zamak3 is thicker;

Figure 3 Zamak12 Figure 4 Zamak3

2) From the comparative observation of cross section Zamak12 and Zamak3, Fig. 3 has finer grains, grayish white color and smaller shiny spots than Fig. 4; Figure

4. Dark and bluish, the appearance of coarse particles is due to the fact that the aluminum and copper element Zamak12 is higher than Zamak3

Organizational structure;

Fig. 5 Zamak12 Fig. 6 Zamak3

3) From the comparative observation of ingot appearance Zamak12 and Zamak3, the surface of Figure 5 is white and the heat shrinkage trace is wider than that of Figure 6

It is the factor of high aluminum base, high melting point, fast solidification and wide shrinkage range.

2、 Segregation during casting of melting ingot

1. In the ingot production process, because the specific gravity of aluminum and parent zinc is much lighter, the aluminum component is easy to separate from the floating surface in the smelting process. Therefore, the placing ingot needs to be stirred to reduce the segregation extent of aluminum component in the pouring as much as possible;

2. Composition and metallographic diagram during initial ingot casting:

1) Sampling a batch of products, from the pattern in Figure 7, the organizational structure is thicker than the leaf in Figure 8, which is the factor of low aluminum composition; During ingot casting, the alloy liquid is poured from the bottom of the furnace. Because the proportion of aluminum component is less than the density of zinc, the aluminum element is light and easy to precipitate to the upper surface, so the aluminum component at the bottom is less than that at the upper part;

Figure 7: Phase diagram of aluminum low segregation

2) Sampling inspection during production. When a batch of ingots is placed at the beginning, the sample composition test is shown in Table 1. Refer to ASTM B240-10

The standard aluminum content is 10.93% of the lower limit;

Table 1 Low Segregation Composition of Aluminum Element

sample name	Element content
	Aluminum (Al)%	Copper (Cu)%	Magnesium (Mg)%	Iron (Fe)%	Cadmium (Cd)%	Tin (Sn)%	Lead (Pb)%	Nickel (Ni)%
Zamak12	ten point nine three	zero point nine five	zero point zero two six	zero point zero two seven	zero point zero zero zero four	zero point zero zero zero five	zero point zero zero three two	zero point zero zero zero eight

3. End of placing

3. Composition and metallographic diagram at the end of a batch of ingots

1) From the pattern in Figure 8, the microstructure is smaller than that in the figure, which is the reason for the high segregation of aluminum composition. The aluminum composition is high, and the alloy grain structure is delicate;

Figure 8: Phase Diagram of Aluminum High Segregation

2) At the end of sampling inspection of a batch of casting ingots, the sample composition test is shown in Table 2, referring to ASTM B240-10

The standard aluminum composition is 11.45% higher than the upper limit

Table 2 High Segregation Composition of Aluminum Element

sample name	Element content
	Aluminum (Al)%	Copper (Cu)%	Magnesium (Mg)%	Iron (Fe)%	Cadmium (Cd)%	Tin (Sn)%	Lead (Pb)%	Nickel (Ni)%
Zamak12	eleven point four five	zero point seven five	zero point zero three one	zero point zero three two	zero point zero zero zero six	zero point zero zero zero eight	zero point zero zero two nine	zero point zero zero seven

3、 Effect of Aluminum Segregation of Zamak12 on Die Casting

1. Influence of low aluminum and high aluminum on operating temperature:

1) When the aluminum content is low, the alloy water can be controlled between 460 ℃ and 470 ℃ in die casting production;

2) The thermal parts of die-casting machinery are relatively durable and resistant to corrosion;

3) Low temperature die casting, reducing shrinkage cavity;

4) Reduce mold overheating and ensure smooth demoulding of products;

5) With high aluminum content, the alloy liquid must be controlled at 470 ℃~490 ℃, and the weak points have opposite defects to those in points 2), 3) and 4) above.

2. Influence of Composition on Die Castings

1) When aluminum is high, the density is smaller, and the size tends to be smaller due to the larger shrinkage;

2) When aluminum is low, the product is overweight, the strength is insufficient, and the anti damping and anti creep properties are reduced;

3) Aluminum segregation is 10~20 ℃ higher than the hourly working temperature of aluminum, which relatively affects the forming of blank, and equipment and process equipment are vulnerable.

3. Defects of blanks in production process and countermeasures

1) Zamak12 zinc alloy has a large melting point, high working temperature and many hot air holes. The solution is to scientifically set the water channel, use an oil temperature machine to equalize the temperature of the mold cavity through the water channel, so as to make the mold filling smooth and full and reduce mold sticking;

2) The aluminum composition is large, the die casting is easy to hot crack, and the die casting is easy to lack materials. The filling gate and inner gate must be scientifically opened and adjusted according to the structure and shape of the product;

3) During die casting production, the mold cavity is prone to heat corrosion and sticking, and the thimble is prone to burn and break, which is caused by overheating and stress concentration. To reduce this phenomenon, the release agent of high polymer water-based materials can be scientifically selected, and properly thickened for production and spraying;

4) The tapping needle is easy to break, which is caused by the high working temperature of raw materials. Drilling can be used for deep holes.

4、 Application scope and performance advantages of Zamak12 zinc alloy raw materials

1. Advantages:

1) Under the same weight, the quantity of Zamak12 zinc alloy die castings can be increased by more than 2% compared with Zamak3, which is the advantage of lightweight and green production;

2) The production cost is smaller than that of aluminum alloy and magnesium alloy die castings, the forming process is relatively simple, and the production efficiency is high;

3) The surface treatment process is mature and the cost is low, and the edges and corners of the product structure are clearer than those of aluminum alloy;

4) The castings have good strength;

5) It has longer service life than aluminum and magnesium alloy die castings.

2. Scope of application: automobile parts, mobile phone shells, centrifuge products, hollow handicrafts, toys, models, etc;

3. The trend of Zamak12 zinc alloy:

1) The cost of magnesium alloy is too heavy and aluminum alloy has forming limitations. Zamak12 zinc alloy die casting process obviously has advantages;

2) With the development of science and technology, 3C products have high requirements for damping performance and shockproof performance of accessories. Zamak12 zinc alloy is gradually used in hot chamber die casting production;

3) It is used for die castings with complex shapes, thin-walled parts, smooth surfaces and precise dimensions.

5、 Example:

1. Appearance and built-in parts of mobile phone case

1) Structural features: as shown in Figure 9

a. Wall thickness 0.2~0.35mm;

b. Complex structure;

c. Numerous small bone sites;

d. The perforation holes are complex and numerous;

e. The inner gate is provided with a thin wall with straight edges around;

2) High strength requirements, no deformation;

3) It shall be assembled with the finished product and shall maintain good creep property;

Figure 9

2. Difficulties in die casting:

1) Difficult to fill type is full;

2) Small bone position is easy to be stuck;

3) Ejection is easy to crack and deform;

4) Hot holes are easy to be found at the product and inner gate.

3. Production and raw material selection

1) In the initial production, Zamak3 zinc alloy raw materials were selected for production, and the products were easy to deform and bruise, and the quality was too heavy, which did not meet customer requirements;

2) Zamak12 zinc alloy raw material is selected for the second production. After many process improvements, the product meets the requirements, especially in the use of finished products, which improves the damping and creep resistance.

4. Solution to die casting problems:

1) In the production process, refer to the third solution in Article 3 for die casting difficulties;

2) Understand the function and performance requirements of customers' products, correctly select production materials, and overcome production difficulties;

3) Scientifically deal with the heat treatment process of mold cavity, and reasonably set up product runner.

6、 Conclusion:

From the above material structure and case analysis, it can be seen that the segregation of Zamak12 zinc alloy ingot and the composition high and low segregation affect the material

Different influences of the organization; Ingot segregation has a great influence on die casting production; The paper introduces the countermeasures for blank defects,

The performance advantages of Zamak12 zinc alloy are also analyzed. In general, the technical history of Zamak12 high aluminum base zinc alloy used in die casting

A new breakthrough in history, the die castings have further improved their wear resistance, heat resistance and creep resistance, followed by improved damping performance

The products used in high frequency occasions have good damping effect. Lower strength, hardness, elongation and impact than the processing cost of magnesium alloy products

High toughness, but there are also weaknesses such as equipment hot work pieces and molds are easy to heat corrosion; With regard to the current situation of the industry, in such a severe economic environment

Only products with energy conservation and emission reduction, scientific and technological innovation and green production have the ability to compete; With the wide application of high aluminum zinc alloy,

The technological breakthrough in the field of die casting also requires constant in-depth trial, research, learning and scientific support.