| 摘要 |
PROBLEM TO BE SOLVED: To provide a long-life spark plug for an internal combustion engine with a large thermal stress relaxing effect of a melted and fixed layer and superior adhesive strength between an Ir alloy chip and an electrode base material and its manufacturing method. SOLUTION: In a spark plug for an internal combustion engine, a precious metal chip 1 is bonded to the front end of at least one of a center electrode 2 and a ground electrode with laser welding. The precious metal tip 1 is made of iridium material containing at least Ir with a melting point of not less than 2200 deg.C. A melted and fixed layer 11, which is provided between the precious metal tip 1 and the electrode base material of the center electrode 2, contains not less than 1 wt.% precious metal with a melting point of 1500-2100 deg.C and a linear expansion coefficient of 8-11×10<-6> / deg.C.
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