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3102 3F03 micro-channel flat tubes
Micro channel flat tubes are an important part of all aluminum microchannel heat exchanger of automobile air conditioner. They are the core component carrying refrigerant. They are often prepared by extrusion. The aluminum flat tube formed by hot extrusion often has bending and twisting problems at the outlet of the extrusion die. Therefore, the aluminum flat tube can be used for the assembly of microchannel heat exchanger only after cold rolling and sizing,
The range of cold rolling reduction in cold rolling sizing is usually 2% ~ 10%. In the assembly of heat exchanger, the process of high-temperature annealing will lead to abnormal large grains in the structure of cold-rolled aluminum flat tube, which will lead to the decline of mechanical properties of aluminum flat tube. By adjusting the cold rolling reduction, the strength of the annealed aluminum flat tube can be changed, and the corresponding annealed aluminum flat tube has the lowest strength
The depression is called the critical depression. For example, the critical downforce of 3102 and 3003 alloy aluminum flat tubes is 4% and 6% respectively.
The critical downforce of aluminum flat tubes of different alloys is determined by the differences of work hardening behavior of alloys. The work hardening behavior of alloy materials is affected by various structural characteristics such as solute atoms, grain size and second phase particles. Compared with 3102 aluminum alloy, 3f03 alloy contains higher concentration of Mn element and has excellent corrosion resistance
In addition to corrosion resistance, it is found that increasing the content of Mn in aluminum alloy is conducive to improving the strength of the alloy through solid solution strengthening. At present, there are few studies on the microstructure characterization and work hardening behavior of 3f03 aluminum flat tube, so it is impossible to compare the differences of work hardening behavior between 3102 alloy and 3f03 alloy. The microstructure evolution of metals during cold rolling and annealing is one of the key issues that have attracted continuous attention in industrial production. It is found that after cold rolling deformation, there is residual strain in the structure in the form of dislocation in the alloy. The dislocation structure remaining in the grain structure determines the evolution behavior of the grain structure in the subsequent annealing process. Due to the different work hardening behavior, different grain structure characteristics will appear in the two alloys during cold rolling / annealing under the same conditions.
- (1) the average grain long short axis ratio of 3102 3f03 micro channel flat tubes is 1 5 ～ 1. In the range of 6, the average grain size of 3f03 extruded aluminum flat tube is large. After 5% cold rolling, the grain structure of 3102 aluminum flat tube reinforcement has a high degree of work hardening. After annealing at 600 ℃ / 3 min, abnormal large grains appeared in the microstructure of the two alloy aluminum flat tubes.
- (2) the constitutive model with strain strengthening correction term can accurately calculate the stress-strain curve of 3xxx aluminum flat tube material, and can solve the dislocation density and the average free path evolution of dislocations in the process of unidirectional tension.
- (3) 3102 micro channel flat tubes have higher Si solid solution concentration and smaller grain size, lower dislocation average free path and higher work hardening rate in the process of plastic deformation. Compared with 3f03 extruded aluminum flat tube, 3102 extruded aluminum flat tube has lower critical downforce.