Patent ID: 7030544

Claim:
A spark plug comprising: a metal shell; a center electrode retained within said metal shell to be insulated electrically from said metal shell; a ground electrode which is made of a Ni-based alloy and retained by said metal shell, said ground electrode having a center electrode-facing surface opposed to said center electrode; an Ir-alloy member which is welded to the center electrode-facing surface of said ground electrode and opposed to said center electrode through a spark gap; and fused portions which are formed by welding of said Ir-alloy member to said ground electrode to establish joints between said ground electrode and said Ir-alloy member and include a melted mixture of materials of said ground electrode and said Ir-alloy member, each of the fused portions containing less than 18% by weight of Ir in a range defined inside an imaginary plane coinciding with an outer peripheral wall of said Ir-alloy member before welded to said ground electrode, wherein the center electrode-facing surface of said ground electrode has formed therein a recess in which said Ir-alloy member is embedded, and wherein each of said fused portions extends from an outer side surface of said ground electrode, between the center electrode-facing surface and a surface opposed to the center electrode-facing surface, to inside a portion of said Ir-alloy member located within the recess.