An overview of the main addition methods used for the common alloying additions.   Alloying Element   Comments on Addition Methods B Boron is added to precipitate transition metal impurities such as Ti and V, and so improve electrical properties. It is mainly added as a dilute master alloy. Bi Principally used to enhance machinability, Bismuth is added both as the pure metal and as a dilute master alloy. Cr Chromium has a number of uses including preventing grain growth in Al-Mg alloys, inhibiting recrystallization in Al-Mg-Si and Al-Mg-Zn alloys and as a corrector for Fe to produce a golden color in anodizing. The main addition technique is as a concentrated tablet or briquette, although a significant quantity is also added as dilute master alloys. A less common addition method is powder injection. Cu Copper is mainly added to increase strength. It is added in many forms, the main ones being as pure metal or master alloys, but concentrated tablets and powder injection are also used. Fe Iron improves high temperature strength. Addition methods include concentrated products, master alloys, pure metal and powder injection. Mg Magnesium provides high strength with good ductility, together with excellent corrosion resistance and weldability.  It is mostly added as the pure metal, although master alloys are also widely used. Mn Manganese improves strength and also plays a role in preventing recrystallization. The main addition techniques are concentrated tablets or briquettes, powder injection and to a lesser extent master alloys. Pb Lead is principally used to enhance machinability. The main addition method is the pure metal, although concentrated tablets and master alloys are also used. Si Silicon is used in 'foundry alloys' as it gives excellent fluidity in casting. It is also used in extrusion alloys to which it contributes to high mechanical properties. The main addition method is pure metal, but significant amounts are added as master alloys and through powder injection. Sr Strontium is added to modify the eutectic in Al-Si alloys. It is mostly added as a dilute master alloy. Ti Titanium provides an important contribution to grain refinement. The main addition methods are tablets (including 100% Ti) and master alloys. Zn Zinc is used to improve strength. It is almost exclusively added as the pure metal. Zr Zirconium is added to inhibit recrystallization. It is mainly added as a master alloy (up to 15% Zr), but also as a concentrated tablet.