Last Updated on January 2021
White metal (or pot metal) is usually aluminum or a low-temperature zinc-based alloy. The latter is the most common and it’s alloyed with small percentages of tin, copper, aluminum, or magnesium to achieve the desired properties for the intended use.
On its end, aluminum alloys are relatively high temperatures with better mechanical properties than zinc-based alloys.
White metals are used in a myriad of applications. For instance, they are used to create decorative pieces, novelty items, and ornaments. Different types of pot metal are used to make jewelry (both expensive and inexpensive pieces). Depending on the design and nature of the jewelry, white metals may be used alone, in addition to different types of artificial and natural stones, or with some plastic components.
Pot metals are also used to make cheap plated flatware that feels and looks like pricier stainless steel flatware.
White metals can also be used to make machine components. For instance, tin and lead-based alloys are often utilized to make bearings for use in heavy equipment or other applications like wheel bearings in various consumer items such as metal drill press machinery.
In addition, pot metal alloys can be used to create fusible plugs for use in manufacturing equipment. And given their low price, white metals based plugs can be replaced whenever with minimal expense.
Added to the list are wall arts, metallic hangings, figurines, medals, and plaques. They are also widely used as cast forms like die-casting or metal sheets that serve as roofing materials in chemical processing plants
The use of white metals in various productions is beneficial because:
- They are inexpensive, which lowers the cost of raw materials. As a consequence, the resulting products are affordable for everyone.
- They are easy to shape and work with; as such, they can be used to create interesting pieces through bending, shaping, or punch cutting
Classification of White Metals
A white/pot metal alloy may contain tin, lead, antimony, cadmium, bismuth, zinc, aluminum, and magnesium. Some of these metals are toxic, as such, not all of the metals listed here are contained in pot metal alloys.
Generally, white metals are categorized into three general groups per their basic compositions, that is, aluminum, magnesium, and zinc. Still, metals are mixed to achieve properties for the intended use. For instance, a base metal for ornaments needs to be polishable and castable with good flow characteristics. It should also have the ability to cast fine details with little porosity and low temperatures of between 230 and 300°C.
As noted earlier, zinc-based alloys are the most common and widely used pot metals. They are low temperature, with low melting ranges. The two types used in welding are:
- Cast zinc
- Rolled zinc
On their end, aluminum alloys comprise small amounts of other metals (such as manganese, magnesium, zinc, and silicon) to enhance their engineering properties.
Physical and Mechanical Properties of White Metals
Pure white metals are ductile, soft yet tough with a high friction coefficient. Their intermetallic compounds are wear-resistant, hard but brittle. As such, they are not ideal to serve as bearing materials.
White metal alloys contain small particles of hard metals embedded in a ductile background of a solid solution. Generally, the ductile elements can wear off, as such, leave the hard compound to carry loads. The wearing off reduces the coefficient of friction – making white alloys suitable for use as bearing elements.
Their mechanical properties include:
- Generally brittle at room temperatures, and as such, require elevated temperatures for better mechanical working.
- The metal surfaces may require mechanically abraded cleaning before spot welding is carried out.
- Lighter in weight.
- Relatively higher electrical conductivity, thermal conductivity, and lower melting points – compared to steel.
- Hard and wear-resistant
- Tough but sufficiently ductile to allow misalignment before running in
- Relatively low coefficient of friction
White Metal Welding
White metals are common due to their cheap castings; however, they are hard to weld because of their alloy content. Think of welding and crossing your fingers in the hope that it holds approach. However, aluminum alloys are relatively easier to weld compared to zinc alloys – especially when TIGGED.
There are welding rods specially made for pot metals. For example, most fabricators report the J.B. weld to be successful. However, be careful when selecting and using the recommended welding rods as white metals are not true alloys. In fact, you’re better off cleaning the broken area of the metal thoroughly, putting a bevel around the circumferences of the broken area, and applying an epoxy.
When welding, keep the following in mind:
The welding flame must be adjusted to carburizing; however, no soot should be deposited on the welded joint. Often, the oxyacetylene flame or plasma cutting is too hot for white metals, as such, select a very small tip. Alternatively, go for a low-temperature solder or look for a superalloy.
When using the torch, be extra careful as the spelter can melt and heat up to melt the solder. In fact, it’s best to first experiment on a broken statue that’s completely useless.
Often, the welding rod is made of pure zinc or a die-casting alloy made of a similar metal as that to be welded. Alternatively, the rod can be using a metal flux (50% of zinc chloride and 50% of ammonium chloride).
When welding, first heat the castings until the base metal liquifies. Then, turn the flame in a parallel direction to the surface. In so doing, you’ll both be keeping the metal soft and heating the rod to attain the same temperature as the metal.
When both the welding rod and the base metal are at the same temperature, apply the rod to and thoroughly fused with the joint walls. Also, manipulate the rod to break up oxides on the metal surface.
Resistance Welding of Rolled Zinc Alloys
Resistance welding is specially designed to weld rolled alloys. It has the least heat input when compared to the gas and arc welding process. It also provides sound welds.
Spot or seam welding is done on lap joints or flanges. Here, the overlap size depends on the thickness of the metal sheet.
Before welding, the working area should be cleaned and degreased (if needed). Cleaning can be done using the following methods:
- Emery board
White metals are used in the context of friction bearing lining metals, such as tin, Inc, lead, and aluminum-based alloys. They are generally referred to as non-copper based, non-ferrous, and non-refractory alloys. Essentially, pot metals or white metals are relatively cheap, low temperature, and low structural strength.