High mechanical strength magnesium alloys and process for obtain

Details High mechanical strength magnesium alloys and process for obtain High mechanical strength magnesium alloys and process for obtain

1989-10-25

1991-03-05

Roy, Upendra

Alloys or metallic compositions

Magnesium base

Aluminum containing

148 115P, 148403, 148420, 419 12, 419 29, 419 33, 420406, C22C 2302, C22C 2304

Patent

active

049976222

DESCRIPTION:

BRIEF SUMMARY
1. FIELD OF THE INVENTION

The present invention relates to magnesium-based alloys with high mechanical strength, and to a process for obtaining them by rapid solidification and consolidation by extrusion. In particular it relates to alloys which contain aluminum and at least zinc and/or calcium, and may contain manganese, with a composition by weight within the following limits: content of impurities:
In particular, it relates to said high mechanical strength alloys having a composition corresponding to that of basic commercial alloys in the prior art, listed in the ASTM standards by the designations AZ31, AZ61, AZ80 (wrought alloys) and AZ91, AZ92 (casting alloys), or G-A3Z1, G-A6Z1, G-A8Z, G-A9Z1 and G-A9Z2 in French standard NF A 02-004; it also relates to alloys having a composition corresponding to these basic commercial alloys to which calcium is added. It should be noted that these alloys contain manganese as an element of addition.


2. STATE OF THE ART

Producing magnesium alloys with high mechanical properties by rapid solidification has already been proposed.
In European Patent Disclosure Document EP 166917, a process of obtaining alloys based on high mechanical strength magnesium has been described, comprising producing a thin ribbon (<100 .mu.m) of alloy by pouring over the rim of a chilled rotating drum, grinding the ribbon thus obtained, and compacting the powder.
The magnesium-based alloys used include from 0-11 atom % aluminum, 0-4 atom % of zinc and 0.5-4 atom % of an element of addition such as silicon, germanium, cobalt, tin or antimony. Aluminum or zinc may also be replaced, at a proportion of up to 4%, with neodymium, praseodymium, yttrium, cerium, or manganese.
The alloys thus obtained have a breaking load on the order of 414 to 482 MPa, an elongation that can attain 5%, and good resistance to corrosion by 3% aqueous NaCl solutions.
In European Patent Disclosure Document EP 219628, high mechanical strength magnesium alloys have also been described that are obtained by rapid solidification, which as alloy elements include from 0-15 atom % aluminum and from 0-4 atom % zinc (having a total of the two of between 2 and 15%), and a complementary addition of 0.2-3 atom % of at least one element selected from the group including Mn, Ce, Nd, Pr, Y, Ag.
However, this process requires the use of non-standard magnesium alloys, including certain elements of addition that are high in cost and often difficult to put into solution and that require that the ribbons obtained in the rapid solidification be ground prior to the compacting.


3. SUBJECT OF THE INVENTION

A first subject of the present invention relates to magnesium-based alloys, consolidated after rapid solidification, having elevated mechanical properties, having a breaking load at least equal to 290 MPa, but more particularly at least 330 MPa and an elongation at break at least equal to 5%, and having the following characteristics in combination:
a composition by weight within the following limits:


______________________________________ aluminum 2-11% zinc 0-12%, preferably 0.2-12% manganese 0-0.6%, preferably 0.1-0.2% calcium 0-7% ______________________________________ content of principal impurities:


______________________________________ silicon 0.1-0.6% copper <0.2% iron <0.1% nickel <0.01% ______________________________________
a mean particle size less than 3 .mu.m;
they comprise a homogeneous matrix reinforced with particles of intermetallic compounds precipitated at the grain boundaries, these compounds being Mg.sub.17 Al.sub.12, optionally Mg.sub.32 (Al, Zn).sub.49, the latter being present when the alloy contains zinc, with contents higher than approximately 2%, and optionally Al.sub.2 Ca when the alloy contains Ca, with a mean size of less than 1 .mu.m and preferably less than 0.5 .mu.m, this structure remaining unchanged after being kept for 24 hours at 200.degree. C.
The alloy must contain at least one of the elements Zn or Ca, or a mixture of the two; when Zn is present, its cont

REFERENCES:
patent: 2264310 (1941-12-01), Hanawalt et al.
patent: 3094413 (1963-06-01), Fisher et al.
patent: 3496035 (1970-02-01), Foerster
patent: 4675157 (1987-06-01), Das et al.
patent: 4718475 (1988-01-01), Das et al.
patent: 4765954 (1988-08-01), Das et al.

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