Metal treatment – Process of modifying or maintaining internal physical... – With casting or solidifying from melt
Reexamination Certificate
2001-05-01
2002-07-23
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
With casting or solidifying from melt
C148S551000, C148S690000
Reexamination Certificate
active
06423163
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a novel free-cutting aluminum alloy which does not contain lead as an alloying element but only as a possible impurity. The invention further relates to processes for the production of such alloy and to the use thereof. The alloy exhibits superior strength properties, superior workability, superior free-cutting machinability, corrosion resistance, requires less energy consumption and is environmentally friendly in production and use. The present alloy is preferably intended to replace free-cutting alloys of the group AlCuMgPb (AA2030).
BACKGROUND OF THE INVENTION
Free-cutting aluminum alloys were developed from standard heat treatable alloys, to which additional elements for forming softer phases in the matrix were added. These phases improve the machinability of the material during cutting by obtaining a smooth surface, while requiring decreased cutting forces and providing decreased tool wear. Chip breakage is also especially improved.
These softer phases are formed by alloying elements that are not soluble in aluminum, do not form intermetallic compounds with aluminum and have low melting points. Elements with these properties are lead, bismuth, tin, cadmium, indium and some others, which are not applicable for practical reasons. Said elements added individually or in combinations are precipitated during solidification in the form of globulite inclusions having a particle size from a few &mgr;ms to some tens of &mgr;ms.
The most important free-cutting aluminum alloys are:
Al—Cu with 0.2-0.6 wt. % Pb and 0.2-0.6 wt. % Bi (AA2011);
Al—Cu—Mg with 0.8-1.5 wt. % Pb and up to 0.2 wt. % Bi (AA2030); and
Al—Mg—Si with 0.4-0.7 wt. % Pb and 0.4-0.7 wt. % Bi (AA6262).
In these alloys, inclusions are formed for the purpose of easier machinability, especially through the use of lead and bismuth. Recently, there has been a tendency to replace lead with other elements because of risks to human health and for ecological reasons. As substitutes, tin and partly indium are most frequently used. The possibility of using tin in aluminum free-cutting alloys has been well-known for a long time. Tin was one of the first elements to be added to aluminum free-cutting alloys in amounts up to 2 wt. %. In practice, the use thereof, on a larger scale, has never taken place because of an alleged impairment of corrosion properties, poorer alloy ductility and high price. Recently, tin has been added, especially to alloys of the groups Al—Mg—Si (AA6xxx series) and Al—Cu (AA2xxx series) containing—when in standard form—lead and bismuth, or lead only.
Alloys with tin should have similar or better properties as to microstructure, workability, mechanical properties, corrosion resistance and machinability in comparison with standard alloys. The formation of suitable chips of alloys with tin depends—similarly as in alloys with lead and bismuth—on the effect of inclusions for easier cutting upon the mechanism of breaking the material during cutting.
Earlier investigations and explanations of the mechanism of breaking chips have been based particularly on alloys containing lead and bismuth. Both elements form softer phases in a harder basis and retain their chemical and metallographic characteristics. At discontinuity sites, cohesion forces are weaker and, thus, the desirable breaking of chips during machining is facilitated. The distribution of globulite phases should be fine and uniform. A simultaneous addition of smaller amounts of two or more elements insoluble in aluminum has a greater effect upon machinability than the addition of one element. The elements are present in globulite phases in ratios equaling the analytical averages thereof.
It is known on the basis of practical experience that the breaking of chips is best at an eutectic composition of the elements insoluble in aluminum. Thus, the opinion prevails that a suitable breaking of chips is a result of the melting of said inclusions at temperatures attained during the working of the material by turning, boring, etc.
SUMMARY OF THE INVENTION
The present invention relates to novel free-cutting aluminum alloys that do not contain lead as an alloy element and further relates to processes for the production of these alloys and to the use thereof. The present alloy possesses superior strength properties, superior workability, superior machinability, corrosion resistance, requires less energy consumption and is environmentally friendly in production and use.
These improved properties and a lowering of the production costs are attained by means of an optimum selection of alloying elements, working processes and thermomechanical treatments.
The present invention provides a free-cutting aluminum alloy containing:
a) as alloy elements:
0.5 to 1.0 wt. % Mn,
0.4 to 1.8 wt. % Mg,
3.3 to 4.6 wt. % Cu,
0.4 to 1.9 wt. % Sn,
0 to 0.1 wt. % Cr,
0 to 0.2 wt. % Ti,
b) as impurities:
up to 0.8 wt. % Si,
up to 0.7 wt. % Fe,
up to 0.8 wt. % Zn,
up to 0.1 wt. % Pb,
up to 0.1 wt. % Bi,
up to 0.3 wt. % total of all remaining impurities, and
c) the balance substantially 100% aluminum.
The alloy containing 1.1 to 1.5 wt. % Sn is preferable.
The alloy containing up to 0.06 wt. % Pb is preferable.
The alloy containing up to 0.05 wt. % Bi is preferable.
The invention further provides a process for working and thermal treatment of the above alloy by semicontinuous casting, homogenization annealing, cooling from the homogenization annealing temperature, heating to the working temperature of extrusion, comprising novel and inventive process measures of carrying out an indirect extrusion at the maximum temperature of 380° C., press-quenching and natural aging.
According to a variant of the above process, the indirect extrusion step is conducted at a maximum temperature of 380° C., press-quenching and artificial aging are conducted at a temperature of from 130 to 190° C. for 8 to 12 hours.
According to a further variant of the above process, the indirect extrusion is conducted at a maximum temperature of 380° C., followed by press-quenching, cold working and natural aging.
According to a further variant of the above process, the indirect extrusion is conducted at a maximum temperature of 380° C., followed by press-quenching, cold working and artificial aging at a temperature from 130 to 190° C. for 8 to 12 hours.
According to a further variant of the above process, the indirect extrusion is conducted at a maximum temperature of 380° C., followed by press-quenching, tension straightening and natural aging.
According to a further variant of the above process, the indirect extrusion step is conducted at a maximum temperature of 380° C., followed by press-quenching, tension straightening and artificial aging at a temperature from 130 to 190° C. for 8 to 12 hours.
According to a further variant of the above process, the indirect extrusion step is conducted at a maximum temperature of 380° C., followed by press-quenching, cold working, tension straightening and natural aging.
According to a further variant of the above process, the indirect extrusion is conducted at the maximum temperature of 380° C., followed by press-quenching, cold working, tension straightening and artificial aging are conducted at a temperature from 130 to 190° C. for 8 to 12 hours.
A further object of the invention is a product obtained according to the above process or variants thereof, having a tensile strength of 293 to 487 N/mm
2
, a yield stress of 211 to 464 N/mm
2
, a hardness HB of 73 to 138 and an elongation at failure of 4.5 to 13%.
A further object of the invention is a product obtained according to the above process or variants thereof, having a tensile strength of 291 to 532 N/mm
2
, a yield stress of 230 to 520 N/mm
2
, a hardness HB of 73 to 141 and an elongation at failure of 5.5 to 11.5%.
DETAILED DESCRIPTION OF THE INVENTION
Alloys made according to the present invention are divided into five groups with respect to their tin content.
1
st
group: 0.40 wt. % Sn to 0.70 wt. % Sn
2
nd
group: 0.71 wt. % Sn to 1.00 wt. % Sn
3
rd
group: 1.01 wt. % Sn to 1.30
Dragojevi{haeck over (c)} Vuka{haeck over (s)}in
Sla{haeck over (c)}ek Edvard
Smolar Toma{haeck over (z)}
Smolej Anton
Impol Aluminum Corporation
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
Wyszomierski George
LandOfFree
Process for the manufacture of a free-cutting aluminum alloy does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the manufacture of a free-cutting aluminum alloy, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the manufacture of a free-cutting aluminum alloy will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2891866