1. Field of Invention
The invention relates to a process for producing aluminum-coated metallic material.
2. Description of the Prior Art
A known process for coating steel wire with aluminum, for example, comprises drawing a cleaned steel wire, which is coated with a flow medium, through an aluminum bath. This process creates brittle intermetallic compounds in the steel-aluminum interface, which sharply limit the use of such wire. Furthermore, the resulting coating is very thin.
Another known process by which steel wire is coated with aluminum is an extrusion process which is not very feasible because it is only possible to bond metals at very low production speeds.
A process for plating steel wire with aluminum is taught in U.S. Pat. No. 3,167,857, wherein a lengthwise moving aluminum band is continuously formed around a steel wire, and is bonded to it by a pair of pressure rollers. The steel wire is coated with zinc, because it is easier to subject zinc to a diffusion bond with aluminum, than steel. In addition, the steel wire is heated to between 200.degree. and 300.degree. C. The aluminum band is brush-polished to remove any oxide film. This process is not suited for continuous operation, since sustained brushing is not possible, because the brushes wear out and add to the abraded material. Also, because aluminum has a high affinity for oxygen, the exposed aluminum metal surface could oxidize suddenly, which may result in brittle intermetallic compounds in the steel-aluminum interface.
A similar process is taught by German Patent Document No. DE-AS 1,452,437, whereby the aluminum band is brushed or sandblasted. This process is not very feasible either, for the same reasons as described above.
The `alumoweld` process for producing aluminum coated steel wire is a known process by which a steel wire is covered with aluminum powder which is thereafter ignited. The ignition of the aluminum powder melts the aluminum, which is then deposited as a film on the steel wire. Unfortunately, the disadvantage of this process is that it is relatively costly, and thus leads to correspondingly high prices for aluminum coated wire.