Study on Production Technology of 6082 Aluminum Alloy Extruded Aluminum Profile

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

Medium 6082 aluminum alloy chemical composition see Table 1

2.2 Component Control

6082 aluminum alloy composition has two main characteristics: on the front, contains the appropriate amount of Mn and Cr; second, the content of Mg, 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 and Cr will increase the quench sensitivity of 6082 aluminum alloy. It is easy to produce serious intragranular segregation in the α (Al) phase, resulting in coarse-grained microstructure of the extruded product, and reducing the oxide 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, it is important to determine the content of Mn: the Mn content of 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 contrasting determination of Mn content was 0.6%-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% to 0.80%. The Mg2Si content should be controlled between 1.5% and 1.6%, and the excess Si content should be controlled at around 0.3%.

6082 aluminum alloy actual composition control range see Table 2

2.3 Process Control

Because the 6082 aluminum alloy is characterized by the refractory metal Mn, the presence of the appropriate amount of Mn can easily cause segregation within the crystal and plasticity in the solid-liquid region, resulting in insufficient crack resistance, so the casting process needs to pay attention to three main points: front, smelting Care should be taken 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. Cooling water pressure should be controlled in the range of 0.1-0.3MPa.

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.

Because 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. It 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 upper limit (480-500 °C);

(2) the mold temperature is taken as 460 °C, extrusion tube temperature is 440-500 °C;

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

(4) To make the main reinforcing phase of the alloy completely solid solution Mg2Si, it must be ensured 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) The 6082 alloy has a high quenching sensitivity, requires a large quenching strength, and has a fast cooling rate. After the product has exited the front beam, it must be immediately quenched online. 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 see Table 3

5. Aging system

Aging is the latter part of the profile to achieve the required mechanical properties. A reasonable aging system must ensure the performance of the product, but also consider the production efficiency and production cost. Combined with the experimental study, the better aging system for 6082 profiles was defined as: aging temperature 170-180°C, holding time 8h, and the storage time of profiles before aging was not more than 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 optimal control range of Mn content is 0.6% to 0.65%, the Cr content should be controlled below 0.15%, and the total amount of (Mn + Cr) is controlled within the range of 0.70%-0.80%. The Mg2Si content should be controlled between 1.5% and 1.6%, and the excess Si content should be controlled at around 0.3%.

In the extrusion process, extrusion outlet temperature and quenching effect control is the key to ensure product performance, should ensure that the quenching temperature above 500 °C, profile extrusion outlet temperature should be controlled at 500-530 °C, quenching strive for strength, speed fast.