This program will develop zinc-based die casting alloys suitable for processing by the hot chamber die casting process that have improved creep strength. Many applications such as fasteners in automobile underhood applications require zinc alloys to maintain a minimum load under long term loading. The results of a survey of automotive designers and specifiers has indicated the following target properties for an improved generation of zinc casting alloys:
- temperature capability of 140 degrees C, however if this could be increased to 160 degrees C then it would encompass 84.5% of respondent desires.
- creep stress at 4500 psi (31 MPa)
- exposure time of 1,000 hours
- maximum creep elongation under the above conditions: 1% or less
The hot chamber die casting process, by which almost all zinc alloys are cast, is known to be a more efficient casting process than the cold chamber technique used to die cast aluminum and other alloys. The lower casting temperature of zinc alloys allows for greater precision in the cast parts, reducing both energy and materials waste. However the capabilities of zinc die castings are limited with respect to sustaining loads for long times at elevated temperatures. Under such conditions, a slow deformation, termed "creep", occurs. Creep is common in all metal alloys under such conditions, but the commonly used zinc casting alloys are less creep resistant than other higher melting temperature alloys, meaning that the cold chamber die casting process must be used to obtain the benefits of higher creep resistance.
Recent preliminary research has shown promise for development of higher creep resistant zinc alloys. It is clear that development of such alloys would reduce energy consumption, metal waste and therefore the environmental impacts of the metal casting industry. Improvements of zinc alloy capabilities that can use the hot chamber die casting process will also improve the competitive advantage of die casters that apply the anticipated program results versus other materials. These results will be made available to interested U.S. die casters through the proposed technology transfer program.