NL9100565A - ALUMINUM PLATE AND METHOD FOR MANUFACTURING THAT. - Google Patents

Abstract

The invention relates to the manufacture of a soft, highly deformable SSF aluminium sheet with a composition belonging to the AA 5000 series of Al-Mg alloys with a Mg content of over 0.8% Mg, suitable for deforming purposes such as, for example, the manufacture of bodywork parts for cars by pressing. The grain size of the sheet after recrystallization annealing at finished thickness is less than 50 mu m. This recrystallization annealing is performed in a continuous annealing furnace with a heating rate of over 50 DEG C/s, followed by quenching. <IMAGE>

Description

ALUMINUM PLATE AND METHOD FOR MANUFACTURING THAT

The applicant mentions as inventor:

Ir. Paul Mariette Clement NEUTJENS in WESTMALLE, Belgium

The invention relates to a soft highly deformable SSF aluminum sheet with a composition belonging to the AA 5000 series of Al-Mg alloys with a Mg content of more than 0.8% Mg, suitable for deformation purposes such as for example the manufacture of body parts for automobiles by presses. The invention also relates to a method for manufacturing the aluminum plate.

For the plate mentioned in the opening paragraph, soft is understood to mean the delivery condition of the plate. In the context of this application, the delivery condition soft includes not only the condition after the recrystallizing annealing, but also that after subsequent light post-processing such as cold rolling and / or smoothing or stretching.

In the context of this application, plate is not only understood to mean plates obtained by cutting to length, but also strip-shaped plate on a roll as long as it has not yet been cut.

In the context of this application, SSF (Stretcher Strain Free) is understood to mean that the plate is free from Stretcher Strain marks type A, so-called Lüder lines, in the case of cold-plastic deformation. This | Flame-like irregularities in the surface of the material occur when the material flows and are not acceptable for visible body parts as they remain visible after painting.

Lüder lines are also known with steel. Deforming steel is usually cold-rolled for this purpose. This is not common with aluminum, because this cold reinforcement significantly reduces the formability.

The 5000 series Al-Mg alloys are very sensitive to Lüder lines when soft. The classic way to desensitize the material to Type A Lüder lines in Al-Mg alloys is to ensure that the grain size of the material at final thickness is greater than 50 μπι. With a grain size of more than 50 μπι the chance of Lüder lines of type A is small. This is achieved by recrystallizing the material at a thickness greater than the final thickness, so-called recrystallizing. In a second cold rolling step, the material is brought to final thickness with a precisely determined reduction in the range of 15 to 20% and recrystallized, so-called final annealing. With a larger reduction, the grain size is less than 50 μπι and Lüder lines occur. With a smaller reduction, the grain size of the material after recrystallization becomes so large that the so-called orange peel phenomenon occurs during pressing. All in all, the classical way of manufacturing SSF Al-Mg sheet is a rather critical procedure that can easily lead to complaints from customers of the sheet due to Lüder lines or orange peel after processing the sheet.

The object of the invention is to provide an improved SSF-Al-Mg plate material and an improved method of manufacturing it.

This is achieved in the invention in that the grain size of the plate after the recrystallizing annealing to final thickness is less than 50 µm, and preferably less than 40 µm. In this context, grain size is taken to mean the average grain diameter according to ASTM E 112.

To obtain the SSF aluminum sheet, the strip-shaped aluminum sheet is annealed to final thickness in a continuous annealing furnace with a heating rate of the aluminum sheet in the heating section of the continuous annealing furnace more than 50 ° C / sec and preferably more than 80 ° C / sec and the plate is then quenched. Preferably, the aluminum plate is heated homogeneously in the continuous annealing furnace by means of inductive heating. Finally, the cold-rolled plate is preferably annealed to recrystallize only at the final thickness.

Classic material is batch annealed. Surprisingly, it has been found that continuous annealed material, the grain size of which is less than 50 μπι, does not show Lüder lines during cold-plastic deformation. Until now, it has always been believed by those skilled in the art that continuous annealed material would not be Stretcher Strain Free due to the small grain size obtained in continuous annealing.

The invention has many advantages. Firstly, the deformability of the plate according to the invention is considerably better and the elasticity limit is also higher. Due to the small grain size, the material does not show any orange peel when deformed, whereby a very smooth surface aspect is obtained in the deformed zones. Secondly, due to the very short annealing time on the surface of the plate, virtually no oxide layer is formed, so that no discolouration and fewer pressing problems occur. Also, the rolling oil after cold rolling in continuous annealing gives much less problems in that no staining occurs due to partial combustion. Especially when there is no annealing, the energy consumption is much lower and the lead time of the product is much shorter. ,

Example

Tests have been taken with material AA 5051 A; this is a material from the 5000 series with 1.8% Mg and DIN standardized as AlMg 1.8.

The following samples were produced:

Sample Intermediate Annealing Final Annealing 15 Annealing 3) Figures

A - v batch IA

B v v 2) batch 1B

C v v 2) continuously 4) IC

D v continuous 45 1D

15 at final thickness 2) reduction after intermediate annealing, for example 15 to 20% 35 annealing final annealing 45 with a heating rate of more than 50 ° C / sec followed by quenching

Tests were then made, the results of which are shown in Figures 1A to 1D and in the table.

Figures 1A through 1D show the transition from the elastic to the plastic portion of the tensile strain graphs of samples A to D.

It appears that only sample A has a pronounced yield strength (horizontal plateau); This is an indication for the skilled person that Lüder lines can occur during cold-plastic deformation.

Sample B, the prior art material, does not have a horizontal plateau. However, no horizontal plateau is found for samples C and D either.

Sample D is to be considered the major embodiment of the invention.

Table

15 over 50 mm.

The table shows that continuous annealing without intermediate annealing in particular provides a high elongation at break.

In order to establish with certainty the presence of type A lines, a tensile test was carried out in which a strip with a polished surface was drawn perpendicular to the rolling direction. The table shows that type A lines only occur in sample A. The grain size of sample A is less than 50 μπι.

The grain size of sample B is greater than 50 μπι as a result of the intermediate annealing, while the grain size of samples C and D is less than 50 μπι.

Finally, the table shows that with continuous annealing a significantly 7% higher Erichsen value is obtained with the same sheet thickness.

Finally, practical processing tests were carried out. A body part on an industrial press was made from plates of samples B, C and D. No Lüder lines occurred, but the surface of the part made from samples C and D was much smoother than that made from sample B. Most pronounced was the difference in the most deformed areas of the part.

Claims (6)

1. Soft highly deformable SSF aluminum sheet with a composition belonging to the AA 5000 series of Al-Mg alloys with a Mg content of more than 0.8% Mg, suitable for deformation purposes such as for example the production of body parts for automotive presses, characterized in that the grain size of the plate after recrystallizing annealing to final thickness is less than 50 μτα. Aluminum plate according to claim 1, characterized in that the grain size is less than 40 μπι. A method of manufacturing the aluminum sheet according to claim 1 or 2, characterized in that the strip-shaped aluminum sheet is recrystallized at final thickness in a continuous annealing furnace with a heating rate of the aluminum sheet in the heating section of the continuous annealing furnace of more than 50 ° C / sec and the plate is then quenched. Process according to claim 3, characterized in that the plate is recrystallized by annealing at a heating rate in the heating section of the continuous annealing furnace of more than 80 ° C / sec. Method according to claim 3 or 4, characterized in that the aluminum sheet is heated homogeneously in the continuous annealing furnace by means of inductive heating. 6. Process according to claims 3-5, characterized in that the cold-rolled plate is only recrystallized to final thickness.