ALUMINIUM
Abundance and ores
Aluminium is the element with the atomic number 13, symbolised as Al. It belongs to the family of transition metals and is the third most abundant element in the Earth’s crust. In 2023, the leading producers of aluminium were China (66% of global production), India, and Russia*.
Highly reactive, aluminium rarely exists in its pure form in nature. However, it is present in many mineral species and primarily extracted from bauxite, which is characterised by a high alumina content (48-61%) (Al2O3).
The Bayer process isolates alumina from bauxite, which is then refined into pure aluminium through electrolysis. In its pure state, aluminium is highly malleable, fragile, and easily deformed.
Types of alloys and classification
By incorporating specific elements, the metal can be strengthened, allowing for the development of a broad spectrum of properties. Aluminium alloys are categorised into two main families based on the method by which they are processed. Alloys for forging are intended to be mechanically transformed through cold processes (drawing, rolling, forging, etc.). They are used in the manufacture of watch components. The second category comprises casting alloys, often used to produce watch case lugs.
Aluminium alloys intended for forging can be also categorised according to their main additive elements:
- 1000 Series: Aluminium with over 99% purity
- 2000 Series: Main additive element: copper (Cu)
- 3000 Series: Main additive element: manganese (Mn)
- 4000 Series: Main additive element: silicon (Si)
- 5000 Series: Main additive element: magnesium (Mg)
- 6000 Series: Main additive elements: magnesium (Mg) and silicon (Si)
- 7000 Series: Main additive element: zinc (Zn)
Specificity
Aluminium is particularly light and resistant to corrosion. Similar to titanium, aluminium is highly oxidisable. An electrically insulating alumina layer forms on its surface upon exposure to oxygen. The uniformity and thickness of this layer can be induced and controlled by anodising (also known as eloxal). By adding dyes to the suspension during anodisation, aluminium can be coloured in a wide range of shades.
Aluminium is easy to machine and has good electrical conductivity, making it suitable for most manufacturing methods, including machining, stamping, and electrical discharge machining.
Aluminium was discovered in the early 19th century, initially isolated from alumina through chemical processes at a high cost. The advent of electricity in 1886 enabled the production of aluminium by electrolysis, allowing for industrial-scale production at lower costs. The emergence of new producing countries around 1970 led to a significant reduction in aluminium prices, contributing to its widespread use. The use of aluminium in watchmaking began in the 1980s, particularly for cases and external parts.
Although its use in watchmaking is relatively limited, aluminium is extensively incorporated in tool manufacturing (fixtures, handles, etc.). It is also a component of numerous alloys. Since the 1980s, aluminium has been used in the production of watch cases. Certain aluminium alloys are also used to manufacture hands and even parts of regulating organs, such as balance staffs and balance screws.