Spark plug

A spark plug comprising:

• a center electrode;
• and
• a ground electrode disposed so as to form a gap between the center electrode and the ground electrode,
• wherein at least one of the center electrode and the ground electrode includes an electrode body, an electrode tip having a discharge surface that faces the gap, and a welded portion formed between the electrode body and the electrode tip and containing a component of the electrode body and a component of the electrode tip,
• the electrode tip includes:
• a tip body comprising a side surface extending in a direction that intersects the discharge surface, and an opposite surface which is disposed on an opposite side of the discharge surface, at least a part of which is in contact with the welded portion and a part of which is a non-contact portion not in contact with the welded portion and
• a cover layer that covers at least the side surface of the tip body,
• the tip body comprises iridium (Ir) or an alloy containing iridium (Ir) as a main component,
• the cover layer comprises an intermetallic compound (IrAl) of iridium (Ir) and aluminum (Al) and having a thickness of 50 μm or less,
• the electrode body comprises an alloy containing 50% by weight or more of nickel (Ni), and
• wherein “Sa” is defined as an area of a section through the tip body along a plane located near but not intersecting the welded portion, and parallel to the discharge surface,
• wherein “Sb” is defined as an area of a projection of the non-contact portion of the opposite surface on the section in a direction perpendicular to the discharge surface, and
• wherein Sa−Sb corresponds to 35% or more of Sa.