Breakthrough of the hottest aluminum alloy medium

Breakthrough of aluminum alloy medium temperature brazing material

this paper briefly describes the process test of 0.8mm thick 5052-H32 aluminum alloy plate. In this test, the semi continuous cast aluminum alloy flat ingot is used to produce 5052h32 aluminum plate for pull rod travel case and bag by hot rolling and cold rolling. After analyzing the test indicators such as material structure and performance, the annealing system of the finished product is determined, and the 5052h32 aluminum alloy plate meeting the mechanical properties and bending requirements of customers is produced

5052 aluminum alloy is a typical alloy in the five series of alloys. The main element is magnesium, and a small amount of Mn, Cr, Ti and other alloy elements are added. It is a heat-treatment unreinforced aluminum alloy. It has the characteristics of medium strength, good plasticity, corrosion resistance, weldability and easy processing and forming. It is 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 appliances, the demand for aluminum used in trolley travel bags is gradually increasing. 5052 aluminum alloy is favored by travel bags because of its good strength, plasticity, welding performance, corrosion resistance, lightweight and other advantages

it is particularly important to optimize the production process in the cold rolling process to meet the strength and excellent stamping and bending properties of aluminum alloy plates for pull rods, luggage and suitcases. After hot rolling and cold rolling of 5052 alloy flat ingot, two test schemes are formulated. The thin film material is a two-dimensional material composed of atoms, molecules or ions deposited on the surface of the substrate. Through the experimental analysis of material annealing, microstructure and properties, a reasonable process system is determined, in order to achieve the best performance, and provide theoretical data support for the next batch production of 5052 alloy plates that meet the conditions

1 test plan

1.1 test material and test target value

performance target value: tensile strength between 220MPa and 240mpa; The yield strength is 150mpa-175mpa, and the elongation is ≥ 14%; 90 ° bending without cracks. The chemical composition of the test material shall comply with table 1

the test material is 5052 alloy flat ingot cast by our semi continuous casting machine. After sawing and milling, our 2400mm single pass reversible coiling hot rolling machine is rolled into 6.5mm thick alloy coil

1.2 design of test scheme

design two process test schemes, analyze the microstructure and properties of 5052 hot rolling test material, and determine a reasonable process scheme to meet the performance indicators and use requirements of customers

test scheme I: 5052 test material is cold rolled to 0.8mm thick → cleaning and trimming → annealing → transverse shear plate → packaging and warehousing

test scheme II: 5052 test material is cold rolled to 1.15mm thick → cleaned and trimmed → retreated → cold rolled to 0.8mm thick → cleaned and trimmed → stabilized → transverse shear plate → packaging and warehousing

sample the finished products of 5052 test materials and conduct annealing test in the laboratory to determine the reasonable return process of test materials. The small furnace annealing test is carried out at the temperature of 200 ℃ - 350 ℃, and the furnace is discharged for air cooling after holding for 2h. The influence of annealing temperature on its mechanical properties and 90 ° bending properties is analyzed, and the metallographic structure is made to analyze its structure

2 analysis of test results

2.1 effect of annealing temperature on the properties of 5052 alloy

Fig. 1 is the mechanical properties annealing temperature change curve of 5052 test material. It can be seen from Figure 1 that the tensile strength, yield strength and elongation change smoothly when the annealing temperature is in the range of 200 ℃ - 230 ℃; In the range of 230 ℃ - 280 ℃, the tensile strength and yield strength decrease with the increase of annealing temperature, while the elongation increases. In the range of 280 ℃ - 320 ℃, the tensile strength and yield strength tend to be stable, and the elongation increases slightly, and basically tends to be stable. In the range of 320 ℃ - 320 ℃, the tensile strength, yield strength and elongation basically do not change. According to the mechanical property annealing temperature change curve of 5052 test material, the annealing temperature at 265 ℃ - 275 ℃ can meet the mechanical property index of the product

Fig. 1 5052 mechanical properties of test material - annealing temperature change curve

2.2 microstructure analysis

Fig. 2 is a typical polarized microstructure. 5052 alloy strip is rolled to 0.8mm, and the total cold rolling processing rate is 87%, which is equal to the fatigue life of a large number of corresponding fatigue test samples. Analysis shows that the internal grains of the material have been completely broken, and the grains have become slender fibrous deformation texture (see Figure 2a). The annealing temperature is in the range of 200 ℃ - 230 ℃, the annealing of the strip is in the recovery stage, and the internal structure only has the merging process of polygonal subgrain. Annealing temperature is in the range of 230 ℃ - 280 ℃, which shows cold rolling deformation texture and recrystallization of initial nucleation (see Figure 2b). With the increase of temperature, cold rolling deformation texture gradually decreases and recrystallization texture gradually increases. When the annealing temperature is 320 ℃, the original slender fibrous cold rolling deformation texture has been gradually replaced by new equiaxed grains, forming a uniform and fine recrystallization structure (see Figure 2C)

in combination with figure 1, when the annealing temperature increases from 320 ℃ to 350 ℃, the mechanical property guarantee requirements remain unchanged during the gas spring experiments of various models. The analysis shows that the grain size has not grown, but the precipitation of second phase particles (Mn, Fe) al6 and Mg2Al3 occurred in the material, the second phase particles at the sub crystal boundary play a pinning role on the grain boundary, and the second phase particles in the crystal play a dispersion strengthening role, These second phase particles seriously hinder the migration of recrystallized grain boundaries, prevent grain growth, and are conducive to the formation of fine recrystallized grain structures

2.3 comparative analysis of the two schemes

combined with the softening curve (see Figure 1), scheme I adopts the metal temperature of 255 ℃ - 265 ℃/20h for the finished product annealing process; Scheme 2: after the 5052 test material is cold rolled to 1.0mm for intermediate annealing, it is rolled to 0.8mm with a processing rate of 20%, and low-temperature recovery annealing with a metal temperature of 180 ℃ - 200 ℃/20h is adopted. The mechanical properties (see Table 2) and the user's situation after two consecutive stamping on the stamping machine (see Figure 3) were measured. It can be seen from table 2 that after stabilizing the annealing temperature, the tensile and yield strength of scheme II increases, and the elongation decreases slightly. The mechanical property measurement results of the two schemes meet the mechanical property requirements of suitcase materials

however, in the use of downstream customers, it was found that the performance of the test material in scheme I was unstable. Given the same amount of punching pressure on the continuous operation punching machine in the factory, some suitcases produced had local punching cracks (as shown in Figure 3), and the punching process was discontinuous, which seriously affected the production efficiency. In scheme 2, the properties of the tested materials are relatively stable, and there is no crack on the surface after punching. After punching, nearly all aviation fields will achieve a smooth growth process. Therefore, the test scheme II can meet the requirements of users for batch production and stamping

scheme I produces 5052 plate with local stamping cracking. The analysis is due to the cold work hardened Al Mg alloy, due to α (AL) there is supersaturation of Mg in the solid solution, resulting in higher chemical free energy; Cold deformation produces a large number of dislocations, which makes the strain energy higher, leading to the instability of material properties, and its deformation resistance is less than the punch pressure. Scheme 2: the production of 5052 plate is stabilized, which reduces the content of Mg in α (AL) to obtain more stable microstructure and mechanical properties and improve the stabilization effect

3 conclusion

1) when the annealing temperature is between 230 ℃ and 280 ℃, the tensile strength and yield strength decrease with the increase of annealing temperature, while the elongation increases. At the annealing temperature of 280 ℃ - 350 ℃, the tensile strength and yield strength tend to be stable, and the elongation increases slightly and basically tends to be stable

2) using test scheme II (6.5mm thick 5052 hot rolled coil cold rolled to 1.0mm thick → cleaning and trimming → medium retreat → cold rolled to 0.8mm thick → cleaning and trimming → stabilization → transverse shear plate → packaging and warehousing) can meet the mechanical properties and stamping requirements of trolley travel luggage products

references

[1] Xiao Yaqing, Xie Shuishui, Liu Jingan, etc Practical technical manual for aluminum processing Beijing: Metallurgical Industry Press, 2004

[2] Wang Zhutang, Tian Rongzhang Aluminum alloy and its processing manual (3rd Edition) [m] Changsha: Central South University Press, 2005

[3] Liu Jing'an, Xie shuihui Main defect analysis and quality control of aluminum alloy processing products Beijing, metallurgical industry press, 2012