Study on Production Technology of 6082 Aluminum Alloy Extruded Aluminum Profile

1 Introduction

6082 aluminum alloy belongs to Al-Mg-Si series heat-treatable aluminum alloy, with moderate strength and good welding performance and corrosion resistance. It is mainly used for transportation and structural engineering, such as bridges, cranes, roof structures, traffic Cars and transport ships.

In this paper, the 6082 aluminum alloy used in the production of extruded profiles was tested to determine the appropriate casting and extrusion process.

2. Casting process

2.1 Chemical composition

The chemical composition of 6082 aluminum alloy in GB/T3190-1996 is shown in Table 1.

2.2 Composition Control

6082 aluminum alloy composition has two main characteristics: first, contains the appropriate amount of Mn and Cr; second, the content of Mg and Si is relatively high. Among them, Mn, Cr, and other alloying elements can inhibit recrystallization or recrystallization grain growth during the extrusion and the extrusion, and refine grains. However, if the total amount of (Mn + Cr) is too high, coarse second phases containing Mn and Cr may be formed, which impairs the precipitation strengthening effect of the Mg2Si phase and counteracts the effects of hindering recrystallization and grain refinement. At the same time, Mn, Cr elements will increase the quench sensitivity of 6082 aluminum alloy. It is easy to produce serious intragranular segregation in the α (Al) phase, resulting in the coarse-grained microstructure of the extruded product and reducing the oxidation coloring effect of the profile. For the Mg and Si components, the 6082 aluminum alloy promotes strengthening by increasing the amount of excess Si while strengthening the Mg2Si.

Therefore, the focus on the content of Mn was determined by experiments: the Mn content was 0.6% ~ 0.65% and 0.9% ~ 0.95% for comparison. When the upper limit of Mn content was found, the coarse grain structure of the tail part of the product was more and the mechanical properties were lower. Therefore, the optimum range of comparison and determination of the Mn content was 0.6% to 0.65%. The content of Cr should be controlled below 0.15%, and the total amount of (Mn + Cr) should be controlled within the range of 0.70% ~ 0.80%. The Mg2Si content should be controlled at 1.5% to 1.6%, and the excess Si content should be controlled at about 0.3%.

The actual composition control range of the 6082 aluminum alloy is shown in Table 2.

2.3 Process Control

Because the 6082 aluminum alloy is characterized by the refractory metal Mn, the presence of appropriate amount of Mn can easily cause intragranular segregation and plasticity in the solid-liquid region, resulting in insufficient crack resistance, so the casting process needs to pay attention to three points: First, smelting should be Pay attention to control the temperature between 740 ~ 760 °C and stir evenly to ensure that the metal is completely melted, the temperature is accurate, and the composition is uniform. Second, casting should consider that the metal Mn increases the viscosity of the alloy, making it less fluid and affecting the casting properties of the alloy. Casting speed should be properly reduced and controlled within the range of 80~100mm/min. Third, increase the cooling intensity, speed up the cooling rate, in order to facilitate the elimination of intragranular segregation. Control the primary cooling intensity, increase the secondary cooling intensity to reduce the stress concentration produced during casting, and avoid the occurrence of ingot cracking defects. The cooling water pressure should be controlled within the range of 0.1 to 0.3 MPa.

Homogenization annealing

6082 aluminum alloy deformation resistance, high mechanical properties indicators. The homogenization treatment process improves the microstructure of the alloy and achieves three main effects: solid solution of Mg2Si phase; elimination of intragranular segregation; transformation of β (Al9Fe2Si2) phase to α (Al12Fe3Si2) phase and refinement of iron-containing phase particles.

Since the presence of Mn in the alloy can reduce the transition temperature, shorten the transition time, and in order to maintain the alloy extrusion performance and extrusion effect, the use of medium temperature homogenization process, that is, homogenization temperature 555 ~ 565 °C; holding time 6h; cooling rate ≥ 200 °C/h.

4. Extrusion process

4.1 Ingot heating method

Ingot heating adopts industrial frequency induction heating. This heating method is characterized by short heating time, which can reach about 500°C within 3min. The temperature control is accurate and the error does not exceed ±3°C. If heated slowly with a resistance furnace, precipitation of Mg2Si phase will occur, affecting the strengthening effect.

4.2 Extrusion

Comprehensive consideration of the main features of 6082 aluminum alloy, combined with the practical production of extrusion process is as follows:

(1), 6082 alloy deformation resistance, so the ingot heating temperature should be biased upper limit (480 ~ 500 °C).

(2) The mold temperature should be 460°C, and the barrel temperature should be 440 ~ 500°C.

(3) The extrusion speed is controlled within the range of 7~11m/min;

(4) To ensure that the main strengthening phase of the alloy is completely solid solution Mg2Si, it is necessary to ensure that the quenching temperature is above 500 °C, so the profile extrusion outlet temperature should be controlled within the range of 500 ~ 530 °C;

(5), 6082 alloy quenching high sensitivity, requiring quenching cooling intensity, cooling speed, after the product out of the beam immediately must be online quenching. For sections with a wall thickness of 2.5 mm or less, quenching with strong winds may be considered. Profiles with a wall thickness of 2.5 mm or more must be quenched with water mist, and the temperature must be reduced to below 50°C.

(6), 6082 aluminum alloy extrusion straightening, stretching rate should be controlled in the range of 1.0% ~ 2.0%. Extrusion process parameters are shown in Table 3.

5. Aging system

Aging is the last step in a section to achieve the required mechanical properties. A reasonable aging system must ensure the performance of the product, and also consider the production efficiency and production cost. Combined with the experimental study, the best aging system of 6082 profiles is defined as: aging temperature 170 ~ 180 °C, holding time 8h, and the time for pre-aging profile storage does not exceed 8h.

6 Conclusion

According to the characteristics and performance requirements of 6082 aluminum alloy profiles, the above process is more reasonable. In the casting process, the 6082 aluminum alloy composition control focuses on the Mn and Cr content ranges. The optimum control range of Mn content is 0.6% to 0.65%, the content of Cr is controlled to be 0.15% or less, and the total amount of (Mn+Cr) is controlled within the range of 0.70% to 0.80%. The Mg2Si content should be controlled at 1.5% to 1.6%, and the excess Si content should be controlled at about 0.3%. In the extrusion process, extrusion outlet temperature and quenching effect control is the key to ensure product performance, should ensure the quenching temperature above 500 °C, profile extrusion outlet temperature should be controlled at 500 ~ 530 °C, quenching strive for strength, speed fast.