Method for manufacturing a forged piston with reinforced ring groove

A method of producing an aluminum alloy piston for use in an engine and having a ferrous ring reinforcement comprising the steps of:

• providing a generally cylindrical piston slug having a head end and a skirt and formed of an aluminum alloy capable of being age hardened at a temperature less than the operating temperature of the engine to cause a constituent precipitation with a resulting expansion of the alloy, the slug having an annular shoulder between the head end and the skirt with the smaller diameter of the annular shoulder defining the outer diameter of the head end and the shoulder defining an annular surface transverse to the axis of the piston slug,
• solution heat treating the aluminum alloy piston slug,
• rapidly cooling the solution heat-treated piston slug to create a super-saturated aluminum alloy solid solution,
• preheating a ferrous ring to a temperature which is higher than the head end temperature during use of the piston in an engine to expand the ring temporarily and to provide an inner ring diameter larger than the outer diameter of the head end,
• preheating the cooled, solution heat-treated piston slug to a working temperature which is lower than the age hardening temperature of the alloy,
• telescopically assembling the preheated and temporarily expanded ferrous ring on the head end of the preheated piston slug against the shoulder,
• thereafter forging to cause the super-saturated aluminum alloy solid solution to flow axially and transversely to the axis of the piston slug against the preheated and temporarily expanded ferrous ring, and,
• after said step of forging, age hardening the super saturated aluminum alloy solid solution at said age hardening temperature to cause a constituent precipation and therefore a permanent expansion of the aluminum alloy.