Hexagonal close-packed structure

Hexagonal metals like titanium, magnesium, and zinc have few slip planes and hardly deform cold. When welding, this means they become brittle quickly in the heat-affected zone, stress heavily, and crack easily. So make sure you don't cold-form the parts and control the heat well. Titanium and zirconium must be welded under shielding gas, otherwise they pick up oxygen and nitrogen and the weld becomes glassy-brittle. Magnesium is best welded with AC, and clean the joint mechanically beforehand. Zinc should not be welded directly; it evaporates and gives off toxic fumes.