Breakthrough in Aluminum Alloy Mid-Temperature Brazing Materials

[China Aluminum Industry Network] Article published in Lw2016 Proceedings - Author Xing Xiaole, Li Yongfeng, Gao Honghui, Hou Baoping, Wu Guangqi, Liu Hui (China Aluminum Henan Luoyang Aluminum Processing Co., Ltd.)

Abstract: This article briefly describes the process test of 0.8mm thick 5052-H32 aluminum alloy alloy sheet. The test uses semi-continuous casting of aluminum alloy flat ingots, hot-rolled and cold-rolled to produce 5052H32 aluminum plate for trolley travel bags. The analysis of the test indicators such as the organization and performance of the materials, and the determination of the finished product annealing system to meet the customer's mechanical properties and bending The required 5052H32 aluminum alloy plate.

5052 aluminum alloy is a typical alloy in the 5 series alloy, the main element is magnesium, and a small amount of alloy elements such as Mn, Cr, Ti are added. It is a heat-resistant non-reinforced aluminum alloy, with moderate strength, good plasticity, corrosion resistance, and Solderability and easy processing and forming are widely used in petrochemical industry, construction industry, transportation industry and electronic communication industry. With the improvement of living standards and the development of lightweight travel tools, the demand for aluminum for trolley travel bags has gradually increased. The 5052 aluminum alloy is favored by travel bags because of its good strength, plasticity, weldability, non-corrosiveness, and light weight.

How to optimize the production process in the cold rolling process is particularly important to satisfy the strength and excellent press bending performance of the aluminum alloy sheet for the trolley travel bags. 5052 alloy flat ingots are hot-rolled and cold-rolled, and two test schemes are formulated. By analyzing and analysing the material's annealing, structure and properties, etc., a reasonable process system is determined to achieve the desired performance and the next step is batch production. The 5052 alloy sheet satisfying the conditions of production can provide theoretical data support.

1 test plan

1.1 Test materials and test target values

Performance target value: tensile strength at 220MPa-240MPa; yield strength at 150MPa-175MPa, elongation ≥14%; 90° bending without cracks. The chemical composition of the test material should comply with Table 1.

The test material is the 5052 alloy flat ingot cast by our company's semi-continuous casting machine. After sawing, our 2400mm single-pass reversible coiling hot rolling mill is rolled into a 6.5mm thick alloy coil.

1.2 test plan design

Two kinds of process test plans were designed to analyze the organization and performance of the 5052 hot-rolled test material, and a reasonable process plan was determined to meet the customer's performance requirements and requirements.

Test Plan I: 5052 test material cold-rolled to 0.8mm thick → cleaning trimming → annealing → transverse shear plate → packaging storage.

Test Plan 2: 5052 The test material was cold-rolled to 1.15mm thickness → cleaning trimming → retreat → cold rolling to 0.8mm thickness → cleaning trimming → stabilization treatment → transverse shearing → packaging and storage.

Samples of the 5052 test material are sampled and an annealing test is performed in the test chamber to determine the reasonable return process for the test material. Furnace annealing tests were conducted at temperatures of 200°C-350°C, and the furnace was air-cooled after 2h of incubation. The effect of annealing temperature on its mechanical properties and 90° bending performance was analyzed. The microstructure was analyzed and the microstructure was analyzed.

2 Analysis of test results

2.1 Effect of Test Annealing Temperature on Properties of 5052 Alloy

Figure 1 is a graph of the mechanical properties of the 5052 test material - the annealing temperature. From Figure 1, we can see that the annealing temperature in the range of 200 °C -230 °C, the tensile strength, yield strength and elongation change more stable; 230 °C -280 °C range, the tensile strength and yield strength with annealing temperature increases It is in a downward trend, and its elongation rate is on the rise. In the temperature range of 280°C to 320°C, the tensile strength and yield strength tend to be stable, and the elongation rate slightly increases, basically stabilizing. 320 °C - 320 °C range, the tensile strength, yield strength and elongation did not change. According to the mechanical properties of 5052 test material - annealing temperature curve, the annealing temperature of 265 °C -275 °C can meet the mechanical properties of the product.

Figure 1 5052 test material mechanical properties - annealing temperature curve

2.2 Organization Analysis

Figure 2 shows a typical polarizing structure. 5052 alloy strip rolling to 0.8mm, the total cold-rolling processing rate was 87%, the analysis that the internal grain of the material has been completely broken, the grain has become a slender fibrous deformation texture (see Figure 2a). The annealing temperature is in the range of 200°C to 230°C, annealing of the strip is in the recovery stage, and the internal organization only occurs in the consolidation process of the multilateral subgrain. The annealing temperature is in the range of 230°C to 280°C, which shows the recrystallization of the cold-rolled deformation texture and the nucleation (see Figure 2b), and as the temperature increases, the cold-rolling deformation texture gradually decreases, and the recrystallization texture decreases. Structure gradually increased. When the annealing temperature is 320°C, the original slender fibrous cold-rolled textured structure has gradually been replaced by new equiaxed grains to form a uniform and fine recrystallized structure (see Fig. 2c).

Figure 1 shows that when the annealing temperature is increased from 320 °C to 350 °C, its mechanical properties remain unchanged, the analysis that the grain did not grow, but the material inside the second phase occurs (Mn, Fe) The precipitation of Al6 and Mg2Al3 precipitates at the second grain boundary at the subgrain boundary, pinning at the grain boundary, and strengthening the second phase at the grain boundary. These second phase particles seriously hinder the recrystallization grain boundary. The migration prevents the grain growth and facilitates the formation of fine recrystallized grain structures.

2.3 Comparison of the two programs

Combined with the softening curve (see Figure 1), the annealing process for the first option uses a metal temperature of 255°C to 265°C/20h; the second 5052 test material is cold rolled to 1.0mm for intermediate annealing, giving a 20% processing rate to 0.8mm is a low temperature recovery annealing with a metal temperature of 180°C to 200°C/20h. Measured mechanical properties (see Table 2) and the user after two consecutive stamping presses (see Figure 3). It can be seen from Table 2 that the tensile and yield strengths of the second stable annealing temperature increase slightly and the elongation slightly decreases. The mechanical properties of the two solutions meet the requirements for the mechanical properties of the suitcase materials.

However, in the use of downstream customers, it was found that the performance of the experimental material of the scheme was not stable. In the continuous operation of the press on the factory, the same size punching pressure was given, and some of the travel containers produced had local stamping cracking (Figure 3). The process is not continuous and seriously affects production efficiency. However, the performance of the test material of scheme 2 is relatively stable. After the punching, the surface has no cracks and the punching process is relatively smooth. Therefore, the use of test program two can meet the user's mass production stamping requirements.

Part I of the production of the 5052 sheet was partially stamped and cracked. The analysis was due to the cold work hardening of the Al-Mg alloy. Due to the presence of supersaturation of Mg in the α(Al) solid solution, the chemical free energy was high; a large number of dislocations resulted from the cold deformation. The higher strain energy leads to the instability of the material properties, and its deformation resistance is less than the punch pressure. The second production of 5052 plate of scheme II has been stabilized to reduce the supersaturation and dislocation density of Mg in α(Al), thereby obtaining more stable structure and mechanical properties and improving the stabilization effect.

3 Conclusion

1) The annealing temperature is between 230°C and 280°C, and its tensile strength and yield strength decrease with the increase of annealing temperature, while its elongation rate shows an upward trend. Annealing temperature of 280 °C - 350 °C, its tensile strength, yield strength tends to be stable, the elongation slightly increased, the basic tend to be stable.

2) Test plan 2 (6.5mm thick 5052 hot rolled coil cold rolled to 1.0mm thickness → cleaning trimming → retreat → cold rolled to 0.8mm thick → cleaning trimming → stabilization treatment → transverse shearing plate → packaging storage ) It can meet the mechanical properties and stamping requirements of trolley travel bags.

references

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[2] Wang Zhutang, Tian Rongzhen. Aluminum alloy and its processing manual (3rd edition) [M]. Changsha: Central South University Press, 2005.

[3] Liu Jingan, Xie Shuisheng. Analysis and quality control of major defects in aluminum alloy processing products. Beijing, Metallurgical Industry Press, 2012.