US3676111A

US3676111A - Method of grain refining aluminum base alloys

Info

Publication number: US3676111A
Application number: US119946A
Authority: US
Inventors: Peter F Wieser; James E Dore
Original assignee: Olin Corp
Current assignee: Olin Corp
Priority date: 1971-03-01
Filing date: 1971-03-01
Publication date: 1972-07-11
Anticipated expiration: 1989-07-11

Abstract

THE INSTANT DISCLOSURE TEACHES A METHOD OF GRAIN REFINING ALUMINUM BASE ALLOYS. THE METHOD OF THE PRESENT INVENTION COMPRISES ADDING BORON AND TITANIUM TO THE MELT IN SPECIFICALLY DEFINED QUANTITIES.

Description

United States Patent O Int. Cl. C22c 21/00 US. Cl. 75-142 Claims ABSCT OF THE DISCLOSURE The instant disclosure teaches a method of grain refining aluminum base alloys. The method of the present invention comprises adding boron and titanium to the melt in specifically defined quantities.

BACKGROUND OF THE INVENTION Aluminum alloys can be classified based on their castability into two general classes, namely those which are stress sensitive and those who are nonstress sensitive.

Sound bar in nonstress sensitive alloy can be cast at high speeds by using relatively large quantities of water. The as-cast macrostructure of these alloys is not especially important and sound bars can be cast regardless of whether the macrostructure is columnar denritic or equiaxed.

Nonstress sensitive alloys do, however, frequently suffer from the formation of objectionable surface grain boundary cracks.

The stress sensitive alloys, however, present particular problems and special care must be taken in order to cast sound bars. Steep temperature gradient which developed in the ingot during solidification and cooling must be minimized in order to neutralize thermally induced stresses that cause cracking of the bar. In addition, the macrostructure of the bar must be controlled by proper grain refining additions or other suitable means. When a fine equiaxed grain size prevails, sound bar can be produced over a wide range of casting conditions. However, when the structure is columnar denritic, it is virtually impossible to cast sound bar under any conditions.

Accordingly, it is a principal object of the persent invention to provide a method of grain refining aluminum base alloys.

It is a further object of the present invention to provide a method of grain refining both stress sensitive and nonstress sensitive aluminum base alloys.

It is a still further object of the present invention to provide a method which is simple, convenient and easily practiced on a commercial scale.

Further objects and advantages of the present invention will appear from the ensuing specification.

SUMMARY OF THE INVENTION In accordance with the present invention it has now been found that the foregoing objects and advantages may be readily obtained.

The present invention comprises a method of grain refining aluminum base alloys which comprises:

(A) Providing a molten aluminum base alloy material containing iron 0.04 to 2%, silicon 0.02 to 2%, balance essentially of aluminum;

(B) Adjusting the melt to contain from 0.004 to 0.01% boron, preferably 0.004 to 0.006% boron;

(C) adding titanium and additional boron to the melt so that 1) the final titanium content of the melt is from 0.01

(2) the final boron content of the melt is from 0.005 to 3,676,111 Patented July 11, 1972 'ice (3) the titanium to boron ratio in the melt is from 1.4

to 2.2; and (4) the boron unbalance is between with the boron unbalance being determined by the foling relationship Boron unbalance=percent boron in the melt O.46 times percent titanium in the melt DETAILED DESCRIPTION As indicated hereinabove, the present invention is a method of grain refining aluminum base alloys containing iron from 0.04 to 2% and silicon from 0.02 to 2%. Magnesium may be present from 0 to 2%, preferably from 0.3 to 1.4% and copper from 0 to 1.53%, preferably from 0.01 to 1.0%.

The present invention is particularly useful with respect to certain aluminum base alloys which will be described in more detail hereinbelow, such as especially Aluminum Alloy 6201, 5005 and with respect to electrical conductor grade aluminum. The material which has been designated by the American Aluminum Association as electrical conductor grade aluminum has a chemical composition of 99.45% minimum aluminum and an electrical conductivity of at least 61% IACS. The conductivity percentages were established according to the American Society for Testing Materials and are based on an equal volume of the International Annealed Copper Standard (IACS).

Particularly preferred aluminum base alloys which are utilized in accordance with the present invention contain silicon in an amount from 0.02 to 1.3%, optimally from 0.2 to 1.3%, iron from 0.04 to 1%, optimally 0.1 to 0.7%, and copper from 0.01 to 1% and optimally from 0.05 to 0.4%.

The alloys which are preferably utilized in accordance with the present invention preferably also contain magnesium in an amount from 0.3 to 1.4%, they may also contain manganese 0.8% max., chromium 0.35% max., zinc 0.5% max., and others 0.05 each, total 0.15%.

Aluminum Association Alloy 6201, which has an electrical conductivity of at least 52.5% IACS, is a stress sensitive alloy and presents particular casting problems. It has been found that this material responds particularly well to the method of the present invention and is a particularly preferred material in the process of the present invention. The chemical composition of this material as listed with the Aluminum Association is as follows:

6201 Aluminum Elements: Alloy, percent (1) Copper 1 0.10 (2) Iron 1 0.50 (3) Silicon 0.50-0.90 (4) Manganese 1 0.03 (5) Magnesium 0.60-0.90 \(6) Zinc 1 0.10 (7) Chromium 1 0.03 (8) Boron 1 0.0 6 (9) Other elements, each i 1 0.03 (10) Other elements, total 1 0.1 (11 Aluminum Remainder Maximum.

Alloy 5005, which is also a particularly preferred material, contains: iron, 0.70% max.; silicon, 0.40% max.; copper, 0.20% max.; manganese, 0.20% max.; magnesium, 0.5 to 1.1%; chromium 0.10% max; zinc, 0.25% max.; others, 0.05% each, total, 0.15%; aluminum balance.

In accordance with the present invention, the particular aluminum material is provided in molten form.

A small boron addition is made so that the boron content of the melt is from 0.004 to 0.006%, nominally 0.005%. This addition is made in the melting or holding furnace prior to casting. The particular object of this initial boron addition is to precipitate any chromium, zirconium, vanadium or titanium present as insoluble borides since any of these elements in solid solution will reduce the electrical conductivity of aluminum and aluminum base alloys. If the particular melt already contains boron, this addition is not necessary. In accordance with the instant process, one can tolerate up to 0.01% boron initially in the melt.

The next step in the process of the present invention is the addition to the melt of titanium and boron in a particular relationship. The titanium and boron addition must be such that all requirements of this relationship exist in order to obtain proper grain refining effect.

The first requirement of the addition is that the final titanium content of the melt be from 0.01 to 0.05%.

The second requirement is that the final boron content of the melt be from 0.005 to 0.02%.

The third requirement is that the titanium to boron ratio is from 1.4 to 2.2.

The fourth requirement of the titanium and boron addition is that the boron unbalance in the melt be between The boron unbalance is determined by using the following relationship:

Boron unba1ance=percent boron in the melt 0.46 times percent titanium in the melt The titanium to boron ratio and the boron unbalance in the melt are related theoretically and are particularly significant. One reason for the particular criticality of these values in the instant process is to prevent the electrical conductivity from being reduced by the presence of titanium which would be in solid solution. Since the stoichiometry for TiB is 2.2. to 1, in order to insure that no titanium is in solution, we prefer to be at this ratio or slightly on the excess boron side. In addition, if the foregoing requirements are met, we find that maximum grain refining is obtained.

The manner of making the titanium and boron additions is not particularly critical and any method known in the art may be utilized for making these additions. For example, the titanium and boron additions may be made by continuously feeding an aluminum-5% titanium-1% boron alloy wire into the melt at a controlled rate as the melt passes through the transfer trough onto the casting.

Naturally, precautions should be exercised during casting to minimize thermally induced stresses, such as in accordance with US. patent application S.N. 110,938 for Continuous Casting Process For Stress Sensitive Aluminum Alloys by J. E. Dore and W. O. Staufier, filed Jan. 29, 1971.

In accordance with the present invention it has been found that the process of the present invention obtains remarkable grain refining without sacrifice of electrical conductivity particularly with respect to the stress sensitive aluminum base alloys. Cracking in the bars has been found to be virtually eliminated, which has been a particularly troublesome problem heretofore.

The nonstress sensitive alloys are also greatly improved. These materials advantageously do not form surface grain boundary cracks due to the provision of a much finer surface grain by the process of the present invention. By converting from columnar dendritic to equiaxed macrostructure, the hot rolling characteristics are improved by minimizing grain boundary separation. With respect to the nonstress sensitive alloys also, these improvements are obtained without sacrifice of electrical conductivity.

The present invention and the advantages therefrom will be more readily understandable from a consideration of the following illustrative examples.

Example I Commercial grade aluminum pig was charged to a holding furnace and melted. The melt temperature was raised to about 1380 F. Subsequently, sufficient quantities of silicon (added as an aluminum-50% silicon master alloy), magnesium (added as magnesium pig) and iron (added as alumiunm-35% iron master alloy) were added to produce an alloy of the following nominal composition; magnesium 0.65%, silicon 0.60% and iron 0.20%. On analysis, the boron content of the melt was found to be 0.002% instead of the desired nominal level of 0.005%. Hence, additional boron as an aluminum-3% boron master alloy was added to the holding furnace to adjust the boron level. The melt was stirred for 10 minutes and then allowed to cool to a temperature of about 1340 F. At this point, a composition check showed that the melt contained 0.005% boron and 0.001% titanium.

The tap hole of the holding furnace was open, the melt allowed to flow to the direct chill casting unit and casting started. Shortly after the start of casting, samples taken from the cast bar revealed a coarse columnar dendritic macrostructure and cracks in the center of the bar. Subsequently, additional titanium and boron were added to the flowing metal stream in the transfer trough by continuously feeding A" diameter aluminum-5% titanium- 1% boron wire at a rate to add about 0.02% titanium. Analysis of the cast bar showed 0.021% titanium and 0.0105 boron. Under these conditions, the titanium to boron ratio was 2.0 and the boron unbalance was 0.0105 -0.46 0.021 or about +0.00l%. The resultant cast bar produced under these conditions had a fine equiaxed macrostructure and was free of cracks and was internally sound.

Example II Example I was repeated using the same alloy and procedure as described except that the intial boron content of the melt was determined to be 0.003% and an addition of 0.004% boron was made to the melt as an aluminum-3% boron master alloy. At this point, the boron content of the melt was 0.007% and the titanium content of the melt was 0.001%. During casting, additional titanium and boron was added to the flowing molten metal stream in the transfer trough continuously in the form of aluminum-5% titanium-1% boron wire as in Example I to add 0.015% titanium.

The final boron content of the alloy was 0.010% while the titanium content was 0.015% as determined by analysis. This provided a titanium to boron ratio of 1.5 and a boron unbalance of 0.0l0-0.46 0.015 or about +0.003%. As in Example I, the resulting cast bar had a fine equiaxed macrostructure and was internally sound and free of cracks.

Example 111 Example I was repeated with the same alloy, except that the initial melt sample showed 0.01% boron. No boron addition was made to the melt. During casting, an addition of aluminum-5% titanium-1% boron wire was continuously fed into the flowing metal stream in the transfer throughs at a rate to add 0.01% titanium. Analysis of cast bar samples showed 0.01% titanium and 0.012% boron present. This gave an unfavorable titanium to boron ratio of 0.83 and an unfavorable boron unbalance of 0.0l20.46 0.01 or about +0.0074%. As expected, the resultant bar had a coarse columnar dendritic macrostructure and contained numerous and severe internal cracks.

Example IV Example III was repeated except that additional aluminum-5% titanium-1% boron was added to the flowing molten metal stream in the trough as wire so as to provide a total titanium content of about 0.04%. The new conditions yielded a final composition containing about 0.035% titanium and 0.017% boron. The titanium to boron ratio was now desirably 2.1 and the boron unbalance was 0.0170.46 0.035 or about +0.001%. In this case, the resultant bar had a fine equiaxed macrostructure and was internally sound and free of cracks.

Example V Commercial grade aluminum pig was charged to a holding furnace and melted. The melt temperature was raised to about 1380 F. Subsequently, sufficient copper (added as metallic copper) and iron (added as aluminum-25% iron master alloy) were added to produce an alloy of the following nominal composition; iron 0.65% and copper 0.40%. On analysis, the boron content of the melt was found to be less than 0.001%, instead of the desired nominal level of 0.005%. Hence, an addition of 0.005% boron as an aluminum-3% master alloy was made to the holding furnace to adjust the boron level. The melt was stirred for minutes and then allowed to cool to a temperature of 1340 F. At this point, a composition check showed that the melt contained 0.005% boron and 0.001% titanium. The tap hole of the holding furnace was opened, the melt allowed to flow to the direct chill casting unit and casting started. Shortly after the start of casting, samples taken from the cast bar revealed a coarse columnar dendritic macrostructure. In addition, numerous cracks were detected in the surface of the bar by means of dye check analysis. Subsequently, additional titanium and boron were added to the flowing metal stream in the transfer trough by continuously feeding diameter aluminum-5% titanium-1% boron wire at a rate to add about 0.02% titanium. Analysis of the cast bar showed 0.019% titanium and 0.009% boron. Under these conditions, the titanium to boron ratio was 2.1 and the boron unbalance was +0.0003% Cast bar produced under these conditions had a fine equiaxed macrostructure and the surface of the bar was free of cracks and other defects.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

What is claimed is:

1. A method of grain refining aluminum base alloys which comprises:

(A) providing a molten aluminum base alloy material containing iron from 0.04 to 2%, silicon from 0.02 to 2%, balance essentially aluminum;

6 (B) adjusting the boron content of the melt to provide from 0.004 to 0.01% boron in the melt; (C) adding titanium and additional boron to the melt so that (1) the final titanium content of the melt is from 0.01 to 0.05%; (2) the final boron content of the melt is from 0.005 to 0.02%; (3) the titanium to boron ratio is from 1.4:1 to

2.2: 1; and (4) the boron unbalance is between with the boron unbalance being determined by the following relationship Boron unbalance=percent boron in the melt 0.46 times percent titanium in the melt (D) casting the said melt.

2. A method according to claim 1 wherein the boron content of the melt is adjusted to contain from 0.004 to 0.006% boron in the melt.

3. A method according to claim 2 wherein said aluminum material is a stress sensitive material.

4. A method according to claim 2 wherein said material is a nonstress sensitive material.

5. A method according to claim 1 wherein said aluminum base alloy is electrical conductor grade aluminum.

6. A method according to claim 1 wherein said aluminum material is an aluminum base alloy containing silicon from 0.02 to 1.3%, iron from 0.04 to 1%, copper from 0.01 to 1%, balance essentially aluminum.

7. A method according to claim 6 wherein said alloy contains magnesium from 0.3 to 1.4%

8. A method according to claim 6 wherein said alloy contains manganese 0.8% max., chromium 0.35% max., zinc 0.5% max., others, 0.05% each, total, 0.15%, balance essentially aluminum.

9. A method according to claim 1 wherein said aluminum base alloy is Alluminum Alloy 6201.

10. A method according to claim 1 wherein said aluminum base alloy is Aluminum .Alloy 5005.

References Cited UNITED STATES PATENTS 6/1933 Nock -138 8/1933 Bonsack 75-138 RICHARD O. DEAN, Primary Examiner