The market demand for 6063 aluminum alloy cylinder tubes in T832 condition is huge. Currently, only 6063 aluminum alloy cylinder tubes in T6 condition can be supplied in China. If they can be supplied in T832 condition, the potential of this alloy can be fully exploited. The mechanical properties of T832 state 6063 aluminum alloy tubes, such as tensile strength, yield strength and elongation, are superior to those of T6 state. To ensure the wear resistance, corrosion resistance and dimensional tolerance of the tubes, it is necessary to have the correct processing and production technology system and the oxidation treatment technology system for the inner and outer surfaces of the tubes.
1 Test Scheme
1.1 Test materials and process flow
The analytical values of the chemical composition of the 6063 alloy used in the experiment are shown in Table 1.
1.2 Process Flow
① Melting and casting → Homogenization → sawing → Heating of ingot → Extrusion → tension and stretching → sawing → cold rolling → quenching → Stretching → straightening → sawing → artificial aging → pretreatment → anodizing → sealing treatment.
② There is no cold rolling process. The rest is the same as above.
2 Test Results and Analysis
2.1 Testing of foreign samples
In order to study the various properties of aluminum alloy cylinder tubes, we tested the cylinder tube samples produced by Alcao Company. The specifications (outer diameter × wall thickness) were 152.4mm×3.18mm, φ101.6mm×3.18mm, φ50.8mm×2.14mm, and φ63.5mm×3.18mm respectively. φl9.05mm×1.47mm.
Inner diameter tolerance +0.51mm
0
Outer diameter tolerance +0.11mm;
0.07
Inner surface roughness, 0.168μm;
The thickness of the oxide film on the inner surface is 20.1μm, and that on the outer surface is 23.0μm.
Microhardness of the inner wall: 3008.6MPa, microhardness of the outer wall: 3302.6MPa.
Mechanical properties, σ0.2240MPa, σ b274.4 MPa, δ 12%;
Organizational inspection: No weld was observed in the low-magnification structure, and the high-magnification structure is shown in Figure 1.
As can be seen from Figure 1, the grain boundaries are entirely composed of linear substances, the grains are elongated along the deformation direction, and there are slip lines in some grains, indicating deformation after quenching. Figure 1a has a smaller grain size than Figure 1b.
2.2 Sample Preparation
Twelve pipe raw materials were prepared according to the process in Table 2. Among them, six pipe raw materials were etched, scraped, and rolled into pipes with a specification of φ46mm×1.5mm on a XIIT75 pipe rolling mill (with a rolling coefficient of 3.97 and a cold deformation of 74.8%). Then, together with the remaining pipe raw materials, they were quenched in a vertical air furnace at a heating temperature of 525℃. The holding times were 40 and 30 minutes respectively. The quenching medium was water. The cold deformation after quenching in water and the heat treatment system were selected according to orthogonal tests.
2.3 Analysis of Test Results
The influence of each factor on the mechanical properties of the pipe based on the results of the orthogonal test is shown in Figure 2. It can be seen that with the extension of the standing time after quenching, the mechanical properties do not decline, indicating that its influence on the mechanical properties is not significant. When the cold deformation after quenching is 15% - 20%, the mechanical properties are the best. The aging system is best with a temperature of 160-165℃ and holding for 8 hours, which is consistent with the heat treatment system of general Al-Mg-Si series alloys.
After quenching, cold deformation is applied to create a dislocation network, making the nucleation of the dissolving phase more extensive and uniform, which is conducive to improving the strength and plasticity of the alloy. The 6063 alloy mainly relies on the formation of a dispersed transition phase for strengthening. After quenching of this type of alloy, when it undergoes cold deformation and is then heated to the aging temperature, the desolvation and recovery processes occur simultaneously. Desolvation is accelerated by cold deformation, and the particles of the desolvation phase will become more dispersed due to cold deformation. Therefore, cold deformation before aging will enhance the strength of the alloy. As can be seen from Figure 3a, the grains of the sample are elongated along the deformation direction, and most of the grain boundaries are composed of point-like substances, with no slip lines within the grains. As can be seen from Figure 3b, the grain boundaries of the sample are entirely composed of point-like substances, with relatively coarse grains and a certain directionality, but not as obvious as that in Figure 3a. By comparing the two, it can be seen that the cold deformation before quenching has a certain influence on the grain size, but the tubes produced by both processes meet the requirements of the American MISAB210 standard.
Anodic oxidation process parameters: Sulfuric acid flow rate, 18% - 22%; Oxalic acid concentration, 3% - 5%; Electrolyte temperature: -5 to +5℃; Current density, 2.5A/dm ²; Electrolysis time, 90-100 minutes; Stir vigorously and add an auxiliary cathode to the inner cavity of the pipe.
The technical index test results of the trial-produced pipe materials are as follows: inner diameter tolerance +0.06/-0.05mm, outer diameter tolerance ±0.01mm. Surface roughness: 0.125μm; The oxide film thickness on the inner surface is 25.5μm. The thickness of the oxide film on the outer surface is 26.0μm. The microhardness of the inner wall is 3195MPa, and that of the outer wall is 3411MPa.
3 Conclusion
The trial-produced 6063 aluminum alloy tubes in T832 condition have dimensions, inner and outer surface roughness, mechanical properties and oxide film thickness that meet the American ASTMB210 standard.
(2) The heat treatment process parameters for 6063 aluminum alloy in T832 condition are as follows: after quenching, apply a cold deformation of 15% - 20%, artificial aging temperature of 160-165℃, and hold for 8 hours.
(3) The anodizing process parameters are as follows: temperature 0±5℃, time 90-100min, and current density 2.5A/dm ².
