Zinc-based alloys with improved ductility

Details Zinc-based alloys with improved ductility Zinc-based alloys with improved ductility

1984-10-11

1986-09-02

Rutledge, L. Dewayne

Alloys or metallic compositions

Zinc base

Aluminum containing

420515, C22C 1804

Patent

active

046095292

DESCRIPTION:

BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATION(s)

This U.S. application stems from PCT International Application No. PCT/BE84/00003 filed Feb. 8, 1984.


BACKGROUND OF THE INVENTION

The present invention relates to zinc-based alloys with improved ductility.
The current area of application of zinc-based alloys extends to numerous industrially important applications. Particularly important are zinc alloys for gravity molding.
In the past attempts have been made to improve the properties of such zinc alloys by adding one or more elements to them, in various quantities extending down to very small quantities, with the aim of obtaining alloys suited to the broadest possible range of applications.
For example, a zinc alloy for gravity molding is known which has a tensile strength on the order of 400 MPa. This strength was attained with an alloy comprised of aluminum in the amount of about 27%, and added amounts of copper and magnesium. However, this particular alloy has low ductility as seen by the fact that its standard elongation, when cast under optimum conditions, is 4 to 8%. The same pertains to other known alloys which are comprised of aluminum in the amount of about 35%, with added amounts particularly of copper.


SUMMARY OF THE INVENTION

The object of the present invention is to provide a zinc-based alloy for gravity molding which has improved ductility, in particular which has substantially greater elongation, while at the same time retaining tensile strength at least equal to that of alloys comprised of aluminum in the amount of 27% or 35% by weight.
The composition of the inventive alloy resulted from an unexpected discovery by the Applicant, according to which it is possible to improve:
The ductility of the alloy, by adding small amounts of boron and/or rare earths; or
The tensile strength of alloy, by adding small amounts of titanium, zirconium, and/or strontium; or
Both the ductility and the tensile strength simultaneously, by a judicious combination of the abovementioned additions. viz., the alloy type Zn-Al-Cu-Mg-(B; or B and Ti)


DETAILED DESCRIPTION OF THE INVENTION

According to a first embodiment of the present invention, an inventive zinc alloy additionally comprising aluminum (25 to 40% by wt., of the alloy), copper (0.5 to 5%), and magnesium (up to 0.1%) has a boron content between 5 ppm and 0.1% and preferably between 0.005 and 0.050%.
The effect of boron on the elongation of an alloy of the type of this first embodiment is perceptible beginning at a boron content of about 5 ppm, and increased boron content ceases to improve the elongation when the boron content exceeds about 0.1%.
Within the scope of this invention, an improvement comprises adding titanium to the boron-containing alloy in the amount of 25 ppm to 0.5% by weight, based on the total alloy and preferably 0.005% to 0.050%.
In practice it has been found that the titanium added must reach at least the amount of 25 ppm of the total alloy in order to have a perceptible effect on the tensile strength.
Also, a titanium content above 0.5% contributes negligibly to the tensile strength. i.e., alloy type Zn-Al-Cu-Mg-(B; or B and Ti)
Further, according to the present invention it is also advantageous to combine the addition of boron and titanium in such a way as to simultaneously improve the elongation and the tensile strength of the zinc alloy.
In this connection it has been found advantageous for the boron:titanium ratio to be substantially equal to 1:5.
According to a second embodiment of the present invention, an inventive alloy is comprised of boron and in addition Zr and/or Sr in the amount (total of Zr+Sr) less than 0.1%.
The applicant has found that Zn-Al-B-Zr, Zn-Al-B-Sr, or Zn-Al-B-Zr-Sr alloys with the above-specified additions of copper and magnesium and meeting the other specified criteria display both substantially increased tensile strength and greater elongation than an alloy not comprised of zirconium or strontium.
An alloy of zinc according to this second embodiment containing 25 to 40% aluminum, 0.5 to 5% copper, and up

REFERENCES:
patent: 1490696 (1924-04-01), De Golyer

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