Metals contain metallic bonds and form lattices. A metallic lattice is a three-dimensional arrangement of metal ions. The metal cations are arranged in a sequence to form a linear sheet-like formation. This formation of metallic cations is managed by a sea of valence electrons. The valence electrons of metal cations are called free electrons of lattice due to their freedom in movement across the whole lattice.  

There are electrostatic forces of attraction between metal cations and a sea of free electrons because these electrons are basically the valence shell electrons of metal ions. The formation of metal ions and free electrons can be shown as;

Why are metals malleable

When these metallic substances are pressed or hammered, the layers of cations may slide over each other. This property of metals makes them malleable and ductile i.e. they can be transformed into different shapes like sheets and frames and can also be drawn out into thin wires.

Malleable substances have plasticity through which they resist the effects of applied forces up to a certain limit. The resistance that is applied force is managed alternatively, so, malleable materials turn to sheet-like structures when hammered and pressed.

Similarly, the malleable materials show a property of ductility that is to change into thin wires without breaking when stretched.

Gold, silver, aluminium, lead, and tin, etc are good malleable and ductile materials among elements. An ounce of gold can be stretched to almost 40 miles.