Metal treatment – Process of modifying or maintaining internal physical... – With casting or solidifying from melt
Patent
1993-06-10
1996-03-26
Lacey, David L.
Metal treatment
Process of modifying or maintaining internal physical...
With casting or solidifying from melt
148666, 148667, 148420, 420402, 420407, 420408, 420409, 420410, 420411, 420405, 420406, C22F 106
Patent
active
055017487
ABSTRACT:
Procedure for the production of a thixotropic magnesium alloy by adding a grain refiner combined with controlled, rapid solidification with subsequent heating to the two-phase area. It is preferable to use a solidification rate of >1.degree. C./s, more preferably >10.degree. C./s. It is essential that the solidification takes place at such a speed that growth of dendrites is avoided. Heating to the two-phase area is carried out rapidly in 1-30 minutes, preferably 2-5 minutes. By heating an alloy comprising 2-8 weight % Zn, 1.5-5 weight % RE, 0.2-0.8 weight Zr balanced with magnesium to a temperature in the two-phase area after casting, the structure will assume a form in which the .alpha.-phase is globular (RE=rare earth metal). The size of the spheres will be dependent on the temperature and the holding time at that temperature and they will be surrounded by a low-smelting matrix. It is preferable that the alloy has a grain size of not greater than <100 .mu.m, more preferably 50-100 .mu.m. A grain-refined magnesium alloy comprising 6-12 weight % A1, 0-4 weight % Zn and 0-0.3 weight % Mn also assumes thixotropic properties when heated to the two-phase area. Grain refiners such as Zr or carbon-based agents such as, for example, wax/fluorspar/carbon powder or calcium cyanamide can be used, depending on the alloy.
REFERENCES:
patent: 2976143 (1961-03-01), Sturkey et al.
patent: 3902544 (1975-09-01), Flemmings et al.
patent: 4116423 (1978-09-01), Bennett
patent: 5143564 (1992-09-01), Gruzleski et al.
patent: 5147603 (1992-09-01), Nussbaum et al.
Gjestland Haavard
Westengen HAkon
Lacey David L.
Norsk Hydro a.s.
Vincent Sean
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