Patent ID: 8638029

Claim:
A spark plug for an internal combustion engine comprising: a rod-like center electrode extending in a direction of an axis; a tubular insulator provided externally of an outer circumference of the center electrode; a tubular metallic shell provided externally of an outer circumference of the insulator; a ground electrode disposed at a forward end portion of the metallic shell; and a noble metal tip made of a noble metal alloy and joined to an object member provided at the center electrode and/or the ground electrode; wherein the noble metal tip is joined to the object member via a fusion zone which contains metal components used to form the object member and the noble metal alloy used to form the noble metal tip, when the noble metal tip and the fusion zone are projected along the center axis on a plane which is orthogonal to a center axis of the noble metal tip, a projected overlap region of the noble metal tip and the fusion zone accounts for 70% or more of a projected region of the noble metal tip, the object member contains nickel as a main metal component and contains at least silicon selected from the group consisting of aluminum and silicon, such that the amount of silicon is 0.4% by mass or higher and such that the total amount of aluminum and silicon is 0.5% to 1.6% by mass; the fusion zone is composed of a plurality of fusion spots which are formed continuously through intermittent radiation of a laser beam or an electron beam; three or more fusion spots are overlapped to form multi-fusion spots, and as viewed along a baseline which passes through centers of the fusion spots, a total length of the baseline which passes through the respective multi-fusion spots is 35% or less of the entire baseline.