What is the difference between malleable and ductile materials? I don't understand the difference: both of them crosses the yield point.
Quoting from wikipedia page:
In materials science, ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized by the material's ability to form a thin sheet by hammering or rolling.
Malleability and ductility are similar, but in certain respects depend on opposite factors. For a material to be malleable, the constituent particles must be able to move past each other easily under compression. If the bonds between particles are strongly directional (as in covalent solids such as diamond), resistance to such movement will be great. Likewise, very strong bonding, even if not so directional, would require more force to move adjacent particles away from each other into new positions, hence reducing malleability. Ductile materials must be malleable, they must permit particles to move past each other. On the other hand, ductility also requires a strong cohesive force, because otherwise the material would break easily.