Spark plug for internal combustion engines having an alloy layer between the electrodes and tip ends

摘要

A spark plug for an internal combustion engine including a center electrode, an earth electrode, a metal tip joined by welding to an ignition section of at least one of the center electrode and the earth electrode, and an alloy layer located at a welding portion between the metal tip and the at least one electrode. The metal tip is formed of material highly resistant to heat and wear which is distinct in the coefficient of thermal expansion from the material of the electrodes. The alloy layer is formed to have a thickness of at least about 10 mu , so as to avoid the rupture of the metal tip along the surface thereof adjacent to the welding portion.