EP0140827B1 - Process for the manufacture of fine grain-textured aluminium rolling mill products - Google Patents

Abstract

A process for the preparation of a rolled aluminum product, containing iron as the predominant alloy element, which has a grain size of less than 10 mu m after annealing to at least 250 DEG C., in which an alloy consisting of 0.8 to 1.5% iron, up to 0.5% by weight of each of Si and Mn, the sum of Si and Mn being between 0.2 and 0.8%, up to 0.3% by weight of any other component, the total of other components being no more than 0.8% by weight, and the remainder being aluminum, is casted at a solidification rate of 2.5 to 25 cm/min, the hot plate is cooled to less than 120 DEG C. at a rate of less than 0.5 K/sec and is then cold rolled with a thickness decrease of at least 75% without intermediate annealing, and the final annealing temperature does not exceed 380 DEG C.

Description

The invention relates to a process for the production of aluminum rolled products with iron as the predominant alloying element, which, after final annealing after annealing at at least 250 ° C., have a grain size of less than 10 μm.

“Grain size” means the average diameter of all grains present.

Such small grains in the annealed condition are, among other things, a good prerequisite for high strength or yield strength with good ductility at the same time; this applies to all thickness ranges from millimeter sheet to film a few micrometers thick.

In the case of aluminum rolled products made of alloys known for this purpose, grains in the order of magnitude of 15 to 50 gm are produced after the use of customary manufacturing processes with a final annealing above 250 ° C. In the meantime, a method has become known according to which aluminum-iron alloys are processed into rolled products in such a way that after final annealing in the range between 250 and 400 ° C., grain sizes which are less than 3 gm occur.

However, this process requires the use of special casting machines that allow solidification speeds of more than 25 cm / min. In the usual continuous casting methods, however, the solidification rate is between 5 and 12 cm / min.

The invention is therefore based on the object of providing a process based on low-alloy aluminum-iron alloys which, using the semi-continuous ingot casting plants which are in widespread use, allows the production of rolled products in which the final roll thickness is at an annealing above 250 ° C, the grains are smaller than 10µm.

According to the invention, the object is achieved in that an alloy consisting of 0.8 to 1.5% by weight of iron, each up to 0.5% silicon and manganese, the sum of silicon and manganese between 0.2 and 0 .8%, and other components up to 0.3% each, up to 0.8% in total, the rest aluminum, is cast at a solidification rate of 2.5 to 25 cm / min, after hot rolling with a cooling rate of at least 0.5 K / sec brought to temperatures below 120 ° C and then cold rolled to a reduction in thickness of at least 75% without intermediate annealing and that the annealing temperature at final thickness does not exceed 380 ° C.

Through the selection of the alloy composition and the set-up of three necessary, but easily adhered to, thermomechanical manufacturing regulations, it was possible to define a process for all casting methods that involve solidification speeds between 2.5 and 25 cm / min or films, grain sizes in the range between 1 and 5 µm, but in any case less than 10 µm.

The specified method is less suitable for solidification speeds outside the defined range.

The ratio of deformability to strength can be increased as the final annealing temperature increases. It was found for the alloy range according to the invention that the final annealing temperature must not exceed 380 ° C. in order to avoid grains of more than 10 μm with certainty.

The steps following hot rolling are also critical for the production of fine grains. The tests showed that, in order not to endanger the formation of fine grains, the cooling rate in the area between the hot rolling end temperature and about 120 ° C must not fall below 0.5 K / sec; the cooling rate below 120 ° C is insignificant in this regard. Such cooling rates can be achieved when the strip passes through a water tank or when the strip is cooled by means of intensive air flow.

The first annealing after hot rolling, a final annealing or, if necessary, an intermediate annealing, must not take place at a thickness which is more than a quarter of the final hot rolling thickness.

The proportion by weight of iron must be higher than 0.8%; otherwise grains of more than 10 µm in size are formed after the final annealing. On the other hand, if there is more than 1.5% iron, the eutectic composition is approached; this harbors the risk of forming coarse precipitates during casting, which would seriously impair the deformability.

If the silicon or manganese content exceeds 0.5%, or if the sum of both contents exceeds 0.8%, there is also a risk of coarse precipitates. With a total of both contents below 0.2%, it is difficult to avoid the formation of a grain size of more than 10 µm.

It has proven to be advantageous to set the lower limit for the iron content at 1.1% and that for manganese at 0.25%. At lower contents, grain sizes can occur which are not significantly less than 10 µm. Manganese levels below 0.25% are also more susceptible to corrosion.

The tests showed that a limitation of the Fe / Mn weight ratio between 2.5 and 4.5 has a particularly favorable effect on the fine grain.

Further advantages, features and details of the invention result from the following description of preferred exemplary embodiments.

example 1 Influence of the alloy on thin strips

According to the continuous casting process, ingots of both alloys with a cross section of 412x1000mm are cast at a speed of 10cm / min; the solidification rate was 7 cm / min. The bars were milled over, preheated to 540 ° C and hot rolled to 8mm. The hot rolled strip passed through a water box and was cold rolled to 0.7 mm. At this intermediate thickness, a three-hour annealing was carried out at 350 ° C; then cold rolling to 0.1 mm. After 20 hours of final annealing at 320 ° C the following values were achieved (the mechanical values measured in the rolling direction):

Example 2 Influence of the alloy on foils

Up to 0.1 mm thick, the two alloys were processed in the same way as in Example 1. It was then cold rolled to 13 µm and finally annealed at 280 ° C.

Example 3 Influence of cooling rate after hot rolling

The manufacturing procedure corresponds in one case (AE) to that of Example 1, in the other case (AK) it was modified so that the hot rolled strip was not passed through a water box, but was immediately rewound.

Up to 0.1 mm the above-mentioned alloy was processed as in Example 1. However, the 20-hour final annealing was carried out in one variant (GE) at 320 ° C and in another variant (GK) at 400 ° C.

Example 5 Influence of the degree of cold rolling between the hot rolling thickness and the thickness during the first annealing

Alloy E1 was processed as in Example 1 to and with the water cooling of the hot-rolled strip. The strip was further cold-rolled to 2.8 mm, annealed at 360 ° C for 3 hours, further rolled to 0.8 mm, annealed at 350 ° C for 3 hours, finish-rolled to 0.1 mm and finally, as in Example 1, 20 hours at 320 ° C annealed (KW).

Claims (4)

1. Process for the production of rolled aluminium products with iron as predominant alloy element, which at final thickness, after annealing at at least 250°C, have a grain size of less than 10 f.lm, characterised in that an alloy, consisting of 0.8 to 1.5% iron, up to 0.5% each of silicon and manganese, the sum of silicon and manganese lying between 0.2 and 0.8% and other components up to 0.3% each, total up to 0.8%, remainder aluminium, is cast with a solidification rate of 2.5 to 25cm/min, after the hot rolling is brought to temperatures below 120°C with a cooling rate of at least 0.5K./sec. and then cold rolled to a thickness reduction of at least 75% without intermediate annealing, and in that the annealing temperature at final thickness does not exceed 380°C.

2. Process according to claim 1, characterised in that the utilised aluminium alloy contains more than 1.1% iron and more than 0.25% manganese.

3. Process according to claim 1 or 2, characterised in that the weight ratio of iron proportion to manganese proportion lies between 2.5 and 4.5.

4. Process according to at least one of claims 1 to 3, characterised in that the utilised aluminium alloy, apart from Fe, Si and Mn, contains at maximum 0.1 % of each further constituent.