| 摘要 |
PROBLEM TO BE SOLVED: To improve a junction property of a chip by optimizing a material of relaxation layer in a spark plug that is made via a relaxation layer by resistance welding of the chip composed of Ir alloy having Ir as the main component in the center electrode and/or ground electrode. SOLUTION: In a tip end part 3a of the center electrode 3 composed of Fe based alloy and in an opposing part 4a of the ground electrode 4, the chip 51 composed of Ir alloy having Ir as the main component is resistance welded via the relaxation layer 61 of stratified formation. As for the composing material of relaxation layer 61, the coefficient of linear expansion is made in a range between that of Ir alloy and that of Fe based alloy, and Young's modulus is made as what is smaller than both of these alloys.
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