JPH03134101A - Conditioning of aluminum alloy powder - Google Patents

Abstract

PURPOSE: To obtain Al alloy powder showing excellent mechanical properties as those obtd. by the effect of degassing by separating Al alloy powder treated as suspension in a soln. of prescribed pH composed of an oxidizer and organic or inorganic acid and thereafter executing drying. CONSTITUTION: A soln. composed of an oxidizer (hydrogen peroxide, sodium peroxide, potassium permanganate or chromium trioxide) or the aq. soln. of the oxidizer and organic or inorganic acid (formic acid or phosphoric acid) is prepd. In this soln. of pH<=4, Al alloy powder is treated as suspension. Next, the soln. and the Al alloy powder are separated, and, after that, drying is executed. Thus, the mechanical properties more excellent than those obtd. by the effect of heating in a vacuum, what is called, degassing can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to the conditioning of aluminum alloy powders.

Problem to be Solved by the Invention In powder metallurgy of aluminum alloys, the formation of an oxide layer on the surface of powder particles causes a problem. These oxides form very low oxygen partial pressures and are therefore virtually unavoidable. When storing the powder, the layer continues to increase hydroxide formation. These surface layers form relatively large pieces and thus prevent a reliable bonding of the powder surfaces when processed into compact materials by pressing, forging or extrusion.

Internal defects develop which have a detrimental effect on the mechanical properties of the product.

Currently, almost the only way to reduce the negative effect of surface oxides on mechanical properties is heat treatment of aluminum alloy powders in vacuum, so-called "outgassing". The effect of degassing is that the ductile or stretchable oxide layer formed after atomization covers the brittle oxide layer. In routine processing of aluminum alloy powders into shapes, such as by cold isostatic pressing, degassing, thermoforming and extrusion, this brittle layer has little detrimental effect on the mechanical properties. If not present, or if properly distributed, dispersion hardening will break it into many small pieces exhibiting superior effects on similar properties.

However, comparing the properties of rapidly solidified powders after sintering (compression and compression molding) shows that the degassing process is only a makeshift improvement method, and the full development of the property improvements made to the powder is difficult. It can be assumed that this has not been done.

OBJECTS OF THE INVENTION AND MEANS FOR SOLVING THE PROBLEMS The object of the invention is to provide an aluminum alloy whose compact material exhibits improved mechanical properties compared to those made from aluminum alloy powders treated only by degassing. It is an object of the present invention to provide other methods of powder processing or powder conditioning of powders.

In addition, the oxide layer surrounding the powder particles is modified so that subsequent processing requires lower processing temperatures.

In addition, gas evolution (foam formation) during processing is reduced to a minimum.

According to the invention, this purpose is to treat the aluminum alloy powder as a suspended liquid in an oxidizing agent or a solution consisting of an aqueous solution of an oxidizing agent and an organic or inorganic acid at a ptr of 4 or less, and to dry it after separation of the solution. This is achieved by a characteristic method of conditioning aluminum alloy powder.

This process can be applied to all types of aluminum alloy powder without any limitation. Typical particle sizes for use in the process according to the invention of aluminum alloy powder suitable for further processing are below 100 microns, preferably below 20 microns.

The optimum ratio of aluminum alloy powder to solution used for mixing is I:2 to 2. ], preferably l2.

Hydrogen peroxide is preferably used as an oxidizing agent in the form of a 30% by weight aqueous solution or sodium peroxide (NatO2) or potassium permanganate (KMnO4). A suitable and preferred organic acid is formic acid (HCOo 1-1 ), while orthophosphoric acid has proven particularly preferred as an inorganic acid.

According to the invention, the solution is prepared as follows, and the weight ratio of 30% by weight hydrogen peroxide solution to formic acid is 1:2 to 1:1.
0, preferably l:4; the weight ratio of 30% by weight hydrogen peroxide solution to orthophosphoric acid is from 100:10 to 100:1.
Preferably! +12; weight ratio of sodium peroxide and formic acid is l:5 to 1:3
0. Preferably 1:12; the weight ratio of potassium permanganate to formic acid is from 1:Ioo to 10:100, preferably from 5:1001 to 20% by weight, preferably 5% by weight of the selected orthophosphoric acid in an aqueous sodium peroxide solution. is added and the pH of the solution is below 4, preferably 3; orthophosphoric acid is added to a saturated aqueous solution of potassium permanganate and the pH of the solution is below 4, preferably 3; l to 20 wt. %,Preferably! orthophosphoric acid in an aqueous solution of trioxide to phosphoric acid of from 10% by weight to IO+1 to 10% by weight, preferably 4:1.
or I:4, optimally 1:1.5. In either case, the pH of the solution is 4 or less.

Aluminum alloy powder is added to the solution of the present invention using a magnetic cooler, vibration stirrer or ultrasonic wave for 5 to 60 minutes.
Mix for a minute, then filter. The aluminum alloy powder has a temperature of lO to 100°C, preferably 18 to 25°C.
Processed as a function of the solution used at temperatures in the range of . As a result of the exothermic reaction of the treatment agent on the surface of the aluminum alloy powder, a temperature rise occurs, indicating that the reaction is progressing.

Formic acid/K M n O4 solution shows good results at a reaction temperature of 80 °C. The treated aluminum alloy powder is then dried at a temperature between 80 and 140° C., preferably about 120° C., for at least 10 hours to remove any formic acid or water before further processing.

Effect: This chemical treatment reflects a change in the mechanical properties of the extruded shape. In addition to improving the dispersion of residues (fragments) of the surface oxide layer, heating during processing, especially extrusion,
Less gas is released from the surface oxide layer. The optimum is reached when this outgassing is completely suppressed.

Aluminum alloy powder of the present invention (12-Fe, A&-C
r or l! The effect of the chemical pretreatment of the -S i -based powder) on the properties of the molded body material made from the powder was determined by structural investigations, tensile tests and fracture toughness measurements.

Structural investigations were carried out on the oxide layers of both the aluminum alloy powder itself and the extrusion molds made therefrom using optical microscopy, scanning electron microscopy and transmission electron microscopy. The results revealed a particularly uniform good structure in the extrusion mold and a good dispersion of the oxide layer residue of the former powder particles.

The yield point (0.2% of yield strength), tensile strength and total elongation were measured in a tension test. In each case, it had at least the same strength and at least a 15% improvement in elongation compared to prior art materials that were only vented.

The fracture toughness (K, c value) is [short rod (ro)
d) Measured with J sample. In this case, the improvement due to chemical treatment was more obvious than in the case of the tensile test.

For testing, A (Fe alloy powder (average particle size 15 microns) was placed in a circular rod (diameter extrusion pressurized,
It was molded at 400°C, pressure 1.000 MPa (specific compressive force), and transformation ratio 21:1). The measured fracture toughness for a simply degassed aluminum alloy sample was c = 25 MPa.
・v+n; For chemically treated samples (particularly with 30 wt% hydrogen peroxide/formic acid), K, C = 48 MPa・ν
The method of the present invention is applicable throughout the powder metallurgy of aluminum alloys since the problem of oxide films is present in all aluminum alloy powders.

The chemical effect, depending on the chemicals selected, is based on two steps linked to different methods. The first is that it attacks, dissolves or modifies the surface layer that arises during atomization and storage of the powder, and the second is that some chemicals create a new surface oxidation that has more favorable properties with respect to powder strengthening. Generate layers.

The examples below provide guidance on the implementation of the method. In the example, All with an average particle size of 15 microns
! 8Fe powder was used. In the examples using formic acid as a solvent, l) H was not measured.

In the examples, "formic acid" refers to concentrated formic acid, and hydrogen peroxide refers to
0wt% aqueous solution. In all cases, the progress of the reaction was monitored by monitoring the temperature of the suspension.

Example A, Treatment of Aluminum Alloy Powder with a Mixture of Hydrogen Peroxide and Formic Acid 400 g of formic acid and 100 g of hydrogen peroxide solution were mixed;
After cooling, Ag, Fe powder of 6009 is suspended in this solution. The sample is kept at 20° C. for 30 minutes with constant stirring, then filtered on a Buchner funnel and washed first with formic acid and then with acetone until the pH is neutral. Formic acid can be recovered by distillation and drying with calcium chloride. Approximately 120% of the aluminum alloy powder thus obtained
Dry for 12 hours at °C.

B. Treatment of Aluminum Alloy Powder with Mixture of Potassium Permanganate and Formic Acid The A12aFe powder of 6009 is suspended in 400 g of concentrated formic acid and within 5 minutes the finely ground potassium permanganate of 69 is mixed with vigorous stirring. The suspension was then stirred for about 10 minutes at 8
Heat to 0°C. The suspension was then filtered on a Buchner funnel, washed first with formic acid and then with acetone, and incubated at 110°C for 15 minutes.
Dry for an hour.

Treatment of aluminum alloy powder with a mixture of C9 sodium peroxide and formic acid.
- Dissolve the lium and bring it to room temperature, then suspend the AQ, Fe powders in this solution. The following operations are as described in A above.

D. Treatment of aluminum alloy powder with a mixture of hydrogen peroxide solution and orthophosphoric acid Add the orthophosphoric acid of 39 to the hydrogen peroxide solution of 1009 with stirring, and adjust p) (to 3 or less (glass electrode). Then 100 g of A&aFe powder is added to this solution and stirred for 25 minutes at 18° C. The suspension is then filtered on a Buchner funnel and dried at 120° C. for 11 hours.

E. Treatment of aluminum alloy powder with a mixture of potassium permanganate aqueous solution and orthophosphoric acid
009 is added to a freshly prepared saturated aqueous potassium permanganate solution such that the pH of the solution is 3 or less (measured with a glass electrode).

909 aluminum alloy powder is then added to this solution and stirred for 40 minutes at 20°C. After filtration and immersion of the filter residue in acetone, it is dried at 130° C. for 15 hours.

F. Treatment of aluminum alloy powder with a mixture of sodium peroxide aqueous solution and orthophosphoric acid Orthophosphoric acid is added to a freshly prepared 5vt% sodium peroxide aqueous solution so that the pH of the solution is 3 or less (measured with a glass electrode). . Next, 1059 aluminum alloy powder was heated at room temperature.
Add to this solution and stir at 18-22°C for 25 hours. After filtration and soaking of the filter residue, add 1 aluminum alloy powder
Dry at 20°C for 13 hours.

G. Treatment of aluminum alloy powder with a mixture of water-soluble trioxide versus acid and orthophosphoric acid 10003! 359 trioxide to acid (C
ros) was added. This was then mixed with 50g of 85wt% orthophosphoric acid. As a result, the pH value of the solution became 4 or less. Next, 2509 aluminum alloy powder was added to the solution at room temperature and stirred at 50° C. for 5 minutes. After filtration, the powder was washed with methanol and dried at 77°C for 24 hours.

Claims (1)

[Claims] 1. Aluminum alloy powder is dissolved in a solution consisting essentially of an oxidizing agent or an aqueous solution of an oxidizing agent and an organic or inorganic acid at a pH of 4.
A method for conditioning aluminum alloy powder, characterized in that it is treated as a suspension and dried after separation of the solution. 2. The method of claim 1, wherein the oxidizing agent is hydrogen peroxide, sodium peroxide, potassium permanganate or chromium trioxide. 3. The method according to claim 1 or 2, wherein the acid is formic acid or phosphoric acid. 4. The method according to claim 1, 2 or 3, wherein the aluminum alloy powder has a particle size of 100 microns or less. 5. The method according to claim 4, wherein the aluminum alloy powder has a particle size of 20 microns or less. 6. The weight ratio of aluminum alloy powder to solution is 2:1 and 1
4. The method of claim 1, 2 or 3, wherein the method is between: :2. 7. The method of claim 6, wherein the weight ratio is 1:1. 8. The method of claim 1, 2 or 3, wherein the processing of the aluminum alloy powder is carried out at a temperature between 10° and 100°C. 9. The method of claim 8, wherein said temperature is between 18° and 25°C. 10. The method according to claim 1, 2 or 3, wherein the aluminum alloy powder is treated at 80°C. 11. Aluminum alloy powder to be treated at 80° and 140°C
4. The method of claim 1, 2 or 3, wherein the method comprises drying between 12. Claim 11, wherein the temperature is between 80° and 140°C.
the method of. 13. The method of claim 1, wherein the solution consists essentially of 30% by weight hydrogen peroxide and formic acid in a weight ratio of 1:2 to 1:10. 14. The method of claim 1, wherein the solution consists essentially of 30% by weight hydrogen peroxide and orthophosphoric acid in a weight ratio of 100:10 to 100:1. 15. The solution is essentially 1:5 of sodium peroxide and formic acid.
The method of claim 1 comprising a weight ratio of from 1:30 to 1:30. 16.The solution consists essentially of potassium permanganate and formic acid.
Claim 1 comprising a weight ratio of :100 to 10:100.
the method of. 17. The method of claim 1, wherein the solution consists of an essentially 1 to 20% by weight aqueous sodium peroxide solution with the addition of orthophosphoric acid to adjust the pH of the solution to below 4. 18. The method of claim 1, wherein the solution consists essentially of a saturated aqueous solution of potassium permanganate to which the pH of the solution is adjusted to below 4 by the addition of orthophosphoric acid. 19. The method of claim 1, wherein the solution consists essentially of a 1 to 20% by weight aqueous solution of chromium trioxide with orthophosphoric acid, and the weight ratio of trioxide to acid is from 10:1 to 1:10.