Page 44 - Welding of Aluminium and its Alloys

36 The welding of aluminium and its alloys

beneficial effects on mechanical properties and the aluminium producers
attempt to eliminate these from their products. The main effects of the
alloying elements are as follows:

• Magnesium (Mg) increases strength through solid solution strengthen-
ing and improves work hardening ability.
• Manganese (Mn) increases strength through solid solution strengthen-
ing and improves work hardening ability.
• Copper (Cu) gives substantial increases in strength, permits precipita-
tion hardening, reduces corrosion resistance, ductility and weldability.
• Silicon (Si) increases strength and ductility, in combination with mag-
nesium produces precipitation hardening.
• Zinc (Zn) substantially increases strength, permits precipitation hard-
ening, can cause stress corrosion.
• Iron (Fe) increases strength of pure aluminium, generally residual
element.
• Chromium (Cr) increases stress corrosion resistance.
• Nickel (Ni) improves elevated temperature strength.
• Titanium (Ti) used as a grain-refining element, particularly in filler
metals.
• Zirconium (Zr) used as a grain-refining element, particularly in filler
metals.
• Lithium (Li) substantially increases strength and Young’s modulus,
provides precipitation hardening, decreases density.
• Scandium (Sc) substantially increases strength by age hardening, grain-
refining element particularly in weld metal.
• Lead (Pb) and bismuth (Bi) assist chip formation in free machining
alloys.

3.3 CEN designation system

3.3.1 Alloy composition identification
A full listing of all of the British and European specifications dealing with
any aspect of aluminium alloys, product forms, supply conditions and
welding is given in Appendix A at the end of the book.
There are two methods in the CEN system for identifying aluminium
alloys, one based on the numerical designation adopted by ISO and as
recommended by the Aluminum Association, the other on the basis of
chemical composition. The details of the European system are contained
in the specification BS EN 573. This is divided into four parts as follows:
• Part 1 Numerical Designation System.
• Part 2 Chemical Symbol Based Designation System.