Provided herein are variably flexible (i.e., variably stiff) metal alloys and methods of making the variably flexible (i.e., variably stiff) metal alloys. A variably flexible (i.e., variably stiff) metal alloy is a metal alloy that has areas of differing flexibility (i.e., stiffness, rigidity or elasticity) along a length of the metal alloy when the metal alloy is subjected to a load in use. Also provided herein are methods of making variably flexible (i.e., variably stiff) metal alloys and products including casting a metal alloy and selectively heat treating portions of the metal alloy to achieve predetermined stiffnesses in those portions.