Plutonium in the δ phase (delta phase) normally exists in the 310 °C to 452 °C range but is stable at room temperature when alloyed with a small percentage of gallium, aluminium, or cerium, enhancing workability and allowing it to be welded in weapons applications. The  δ phase has more typical metallic character, and is roughly as strong and malleable as aluminium. In fission weapons, the explosive shock waves used to compress a plutonium core will also cause a transition from the usual  δ phase plutonium to the denser α phase, significantly helping to achieve supercriticality. The plutonium-gallium alloy is the most common δ-stabilized alloy.
Gallium, aluminium, americium, scandium and cerium can stabilize the δ phase of plutonium for room temperature. Silicon, indium, zinc and zirconium allow formation of a metastable δ state when rapidly cooled. High amount of hafnium, holmium and thallium also allows retaining some of the δ phase at room temperature. Neptunium is the only element that can stabilize the α phase at higher temperatures. Titanium, hafnium and zirconium stabilize the β phase at room temperature when rapidly cooled.