5xxx aluminum alloys form Luder bands that appear when processing exterior body panels for automobiles. These Luder bands consist of two types A and B, which will be described later in the paper. They form surface markings from localized flow which appear after forming. These markings are seen with the naked eye, and paint does not adhere well to the surface.
Materials and alloys used in today's aerospace industry must have good mechanical properties. Some properties that are desired by the designers of these alloys are:
the ability to withstand creep,
good oxidation resistance,
light weight,
and high strength and ductility.
Without these properties, a material is useless.
Niobium is a refractory metal that first went into use around 1925 to improve the mechanical properties of carbon, stainless, and tool steels. The two people credited with this discovery are Becket and Franks. They showed that small amounts of niobium, when added to fully killed carbon steel, increased the yield and tensile strength of the alloy. Since then, niobium, because of its properties, has become one of the most important alloys used in the aerospace field. Niobium metal is tough, ductile, low in density and has a unique combination of mechanical and physical properties. It is the lightest of the refractory metals and has very good thermal conductivity. This combination of properties made it a useful material for the rapidly expanding space-exploration program in the late 1950s. A drawback of niobium though is that at temperatures above 1000C, it oxidizes so rapidly in the pure or unprotected form, that it cannot be used in such environments. However there are a number of alloys coated with special silicide coatings that improve the oxidation resistance for use in aerospace applications.
There are several factors which are combining to make the use of aluminum alloys in automobile applications more necessary. The United States Congress has passed CAFE (Corporate Average Fuel Economy) which sets minimum fuel efficiency levels. These mandates currently require an average of at least 27.5 mpg for passenger cars and 21.5 mpg for light trucks. These mileage regulations conflict with other government regulated mandates for safety features such as airbags, side-impact collision beams, and antilock braking systems. Consumer demands for features such as power windows and door locks also reduce fuel efficiency. All of these extra features add significant weight which is detrimental to fuel efficiency. To accommodate these conflicting demands, automobile manufacturers have been looking for lighter materials to use in place of steel. Aluminum alloys appear to be the most promising of the lighter materials available.