| 摘要 |
This spark plug has both a main metal fitting and an earth electrode which has a base part joined to the tip of the main metal fitting. The earth electrode comprises both an outer layer and a core part disposed on the inner peripheral side of the outer layer. The outer layer forms at least a part of the surface of the earth electrode, is joined to the main metal fitting, and is made of a material which comprises nickel as the main component and contains aluminum in an amount of more than 0 to 2.5wt%. The oxygen content of the surface of the outer layer exceeds 0wt% and is up to 8wt%. The core part includes a first layer made of either copper or a material comprising copper as the main component. In a cross section of the base part of the earth electrode, said cross section including the central axis of the spark plug and the central axis of the earth electrode, at least one of the two boundary lines which show the boundary between the outer layer and the core part includes an oblique line which extends from the main-metal-fitting-side end of the boundary line toward the outer periphery side of the outer layer obliquely against the central axis of the earth electrode. |
