A metal with a , having many operable slip systems will be relatively more ductile than one with few or no such systems. For example, magnesium alloys have many operable slip systems and are very ductile.
But titanium has few such structures in its crystal structure (or none at all) so it is relatively more resistant to plastic deformation than magnesium but less resistant than aluminum or copper alloy with plentiful slip systems. A metal will also be relatively more ductile if the grains of crystals that make up the solid are large relative to their size because this facilitates the movement of atoms past one another during plastic deformation operations.
Large-grained metals like steel can therefore deform plastically without breaking when subjected to heavy loads as long as these loads are applied slowly enough for a sufficient number of grain boundaries to separate before they reach yielding point. Alloys that are designed to have ductile features can be made by adding elements of low melting point (e.g., aluminum, silicon) in amounts that will cause the grains of crystals making up the metal solid to grow larger than they would otherwise be if only a single type or smelted mix-metal were used as part of the alloying material.
If an extrusion is not allowed sufficient time for grain growth within its container before being cooled and solidified then it will take on a brittle character because there was insufficient time for any movement between adjacent grains during cooling operations. Tubes manufactured with this technique may subsequently break when subjected to normal working stresses such as those created when pulling them out from their molds.