Technology for recycling magnesium alloy housings of notebook computers

Abstract

Magnesium housings, which are lightweight, strong, and have high heat radiation characteristics, are in widespread use for portable personal computers and similar devices. Another characteristic of magnesium alloy is that it is a metal that can be melted for recycling. There are two ways of recycling magnesium alloy housings, one for recycling excess material generated during the molding process and one for recycling collected magnesium alloy housings that have been painted. Whether the molding method is die casting or thixomolding, the housing weight accounts for only about 30% to 50% of the Mg alloy that is injected. The remaining 50% to 70% is sprue and runner, which are excess after molding. It is important to establish a method of recycling for the excess material by as cost reduction. However, the data available for the material that was recycled repeatedly was not adequate. This was an issue to resolve in promoting the recycling of Mg alloy housings. Notebook PCs collected from the market are encased in painted MG alloy housings. Now, painted Mg alloy housings is rarely recycled. In the former process, adjusting the composition of the magnesium alloy in the remelting process restores the same strength and corrosion resistance characteristics as the virgin material despite repeated recycling. In the latter process, soaking in a solution causes the paint to flake off the magnesium alloy housings. The remaining alloy that is then remelted and the adjusted composition can produce a recycled material having the same performance characteristics as the virgin material without generating much gas or dust in the remelting process. The technology for recycling excess material was first applied to the production of the Fujitsu PC FMV-BIBLO notebook that was marketed in 1999. The technology for recycling painted magnesium alloy housings will be applied in full starting in fiscal 2002.