A piston for an internal combustion engine is provided. The piston includes a lower part joined to an upper part, for example by friction welding with inertia. The upper part presents a combustion surface and an undercrown surface. The piston also includes a cooling gallery surface provided by the upper part and the lower part. The cooling gallery surface surrounds a volume of space for containing a cooling media. The piston can include serrations in the cooling gallery surface and/or undercrown surface to increase surface area and thus reduce the temperature of the piston. The piston can also include shaped weld curls, instead of or in addition to the serrations, which also increase surface area and reduce the temperature of the piston.