Plastic and steel were once the staples in consumer electronics casings. Today, that doesn't seem to have changed. However, many of the new electronics that seem to be sporting a lightweight plastic housing, or strong steel one are actually comprised of neither. Today consumer electronics are made largely of a magnesium alloy.
Magnesium alloy materials closely resemble the special plastics used in electronic casings. The Thixomolding process can create magnesium alloy products that are much thinner than previous plastic and steel models. The alloy is often considered a space-age invention because of its ability to be molded into a very thin material. Magnesium products are finished using carbon fiber, plastic and sand based abrasive materials. The product is buffed, polished, and finished in several steps. Die cast magnesium components can be painted using e-coat or powder coat processes. The parts require a pre-treatment to ensure adhesion. There are several body structure applications in production that are painted as well as first surface interior components. Magnesium alloy materials are cheaper because of its lower diecasting and surface finishing costs. They are higher strength than plastic and have better recyclability properties.
Plastic electronics are created using the injection molding process that is similar to Thixomolding. They can create very thin casings, but not those that are very strong. The plastic is very versatile. It can be died to resemble a metallic material or finished to get the same result. The finished product is very light, but does not stand up to a drop test. The magnesium alloy doesn't crack when dropped, but also goes a step further to protect the components inside the casing.
The best examples of magnesium uses are the laptops being created by Apple. For example, they are thin enough to slip into a manila envelope. They look fragile and are so light that users would swear they were made of plastic. These personal, portable computers are built using magnesium alloy however. In the MacBook Air, the three pounds of computing consists of a frame and casing made of magnesium. Other companies like Toshiba are using the alloy to create their own slim and light versions.
The fact that magnesium alloys have been created to maintain many of the plastic traits is significant in itself. Consider the alloy an improvement on the plastic casing, adding strength, dampening abilities to the thinly molded material.