5754 aluminum sheet for automobiles

5754 aluminum alloy sheet for automobiles

5000 series aluminum alloys have become a popular material for automobile lightweighting due to their excellent specific strength, forming performance, welding performance and corrosion resistance. They have been widely used in the manufacture of automobile engine hood inner panel reinforcements and support parts, door inner panels and structural parts.

5754 aluminum alloy sheet for automobiles

5754 Aluminum Alloy Strip User Technical Requirements

According to the user technical agreement, the use of 5754-O aluminum alloy is the channel guard plate of the automobile, and the finished strip specification is 0.8mm×1185mm×C.

• (1) Chemical composition. The chemical composition of the product shall comply with the provisions of GB/T 3190-2020 “Chemical Composition of Deformed Aluminum and Aluminum Alloy”.
• (2) Mechanical properties. The yield strength Rp0.2 is 90MPa~125MPa, the tensile strength Rm is 190MPa~225MPa, and the elongation at break A50≥20%.
• (3) Surface requirements. The product surface has no appearance defects such as scratches, oil stains, black spots, ripples, etc., and there is no tensile strain mark on the surface after stamping.

5754 aluminum alloy test production process

According to user needs, the 5754 aluminum alloy substrate needs to go through multiple processes such as longitudinal cutting, cross cutting and stamping in the downstream slitting center. Therefore, the material has high requirements for plate shape, mechanical properties and stamping performance, and requires no tensile strain marks on the surface after stamping. In view of the process development and trial production of this product, our company has established a 5754 aluminum alloy process development team for automobiles, and carried out research and development of this alloy in the form of a project team. The following focuses on the analysis and introduction of cold rolling, air cushion furnace finished product annealing and user trial.

The 5754 test material melting and casting process adopts semi-continuous casting production, with a specification of 570mm×1310mm×7400mm. Its alloy composition (mass fraction, %) is measured as Si≤0.03, Fe 0.05~0.15, Cu≤0.04, Mn0.30~0.35, Mg 2.6~3. ０，Cr≤０．０５，Zn≤０．０５，Ti≤０．０２，other single≤０．０５，other total≤０．０５，Al remainder; meet the requirements of user agreement. After sawing and milling, the ingot is supplied for hot rolling production.

5754 aluminum alloy test production process

In the production process of the “1+3” unit of the hot rolling process, the start rolling temperature, the thickness of the intermediate billet, the coiling temperature and the convexity are controlled. The hot rolled coil specification is 4mm×1225mm×C, the cold rolling deformation rate is reserved for 80%, and the finishing trimming amount is reserved for 40mm. The actual measurement of hot rolled coil production shows that the hot rough rolling start rolling temperature is 470℃～480℃, the intermediate billet thickness is 25mm～35mm, the coiling temperature is 320℃～330℃, and the convexity is 0.027.

The hot rolled coil outer ring sample plate was tested for surface anodizing and the rating was B-, as shown in Figure 1, which meets the acceptance requirements of the next process.

1 Cold rolling process production

In order to give full play to the capacity of 2500mm cold rolling mill equipment and reduce production costs, the 5754 aluminum alloy cold rolling process adopts a large reduction rate production, and the pass arrangement is 4mm-2.3mm-1.35mm-0.8mm; that is, 2 passes are rolled to the intermediate annealing thickness, and 1 pass is rolled to the finished product thickness of 0.8mm after intermediate annealing.

The surface roughness Ra of the working roll in the cold rolling process is selected as 0.56~0.60, the surface roughness Ra of the working roll in the intermediate pass is selected as 0.38~0.60, and the surface roughness Ra of the working roll in the finished pass is selected as 0.38~0.42. At the same time, through the rolling mill plate control system, the upper and lower intermediate roller shifting amount of the finished product pass was increased from 120mm to 149mm, further controlling the finished product plate shape to ensure the straightness after the subsequent process of straightening. The finished product plate shape comparison is shown in Figure 2. By increasing the amount of roller shifting, the plate shape guarantee value reaches 100%. The finished product thickness curve in the uniform speed section is shown in Figure 3. The maximum thickness deviation is 6μm, and the thickness difference guarantee value is 97.86%.

In addition, the 5754 aluminum alloy cold-rolled finished product pass must strictly control the oil content on the strip surface. In the actual production process, by increasing the rolling outlet sweeping pressure, sampling and testing the oil content on the strip surface <50mg/m2, it is avoided that the residual oil spots are oxidized at high temperature during the intermediate annealing process due to incomplete cleaning, forming color difference on the material surface, resulting in the surface not meeting user requirements.

2 Annealing process production

The annealing process of 5754 aluminum alloy is divided into intermediate annealing and finished product annealing. The intermediate annealing adopts a two-stage differential temperature control mode with a steady-state temperature of 330℃; the finished product annealing is produced in an air cushion continuous heat treatment furnace with an annealing temperature of 510℃, a process speed of 55m/min, and a tensile straightening elongation of 1%. To verify the influence of different cold rolling rates on the mechanical properties of the finished product after intermediate annealing.

The influence of cold rolling rates after different intermediate annealing on the mechanical properties of 5754 aluminum alloy is shown in Figure 4. As can be seen from the figure, the mechanical properties of Scheme 2 and Scheme 3 meet the user’s technical requirements. With the increase of the cold rolling reduction rate after intermediate annealing, the tensile strength and yield strength of the material show an upward trend, and the elongation shows a downward trend; the cold rolling reduction rate increases from 27.3% to 40.7%, and the tensile strength and yield strength of the alloy material increase by 4.3% and 4.5% respectively, and the elongation decreases by 9.6%. When the cold rolling rate after intermediate annealing is 40.7%, the tensile strength and yield strength of the material reach the maximum value, which are 219MPa and 92MPa respectively. The main reason for the increase in strength is that with the increase in cold rolling deformation after intermediate annealing, the dislocation density in the organization gradually increases.

User Trial

5754 aluminum alloy coils are uncoiled, straightened, longitudinally cut, and transversely cut in the downstream slitting center, and cut into plates with specifications of 0.8mm×375mm×450mm. According to the user’s stamping technical requirements, 100 sets of competitive products were first produced according to normal stamping process parameters. Under the condition that the mold does not make any parameter adjustments, 100 sets of our company’s materials were test-punched. After on-site inspection, the parts have no stretching necking cracks and no tensile strain marks on the surface, which meets the user’s requirements.