A monobloc piston assembly for an internal combustion engine is provided. The piston assembly includes a piston body which extends along an axis and is formed of at least two pieces of material which are joined together at least one friction weld joint which extends continuously through an annular shape around the axis. One of the pieces has an upper surface with a combustion bowl having a rotationally asymmetrical shape around the axis formed therein. Another of the pieces has a dome-shaped receiving surface which is rotationally symmetrical around the axis for slidingly receiving a portion of a connecting rod.