A tip that contains a noble metal is joined to a joining surface of an electrode base material of a ground electrode via a welded portion. On cross-sections of the tip and the electrode base material in a longitudinal direction of the joining surface, the welded portion has a void above the joining surface, and a continuous distance of the welded portion on the joining surface is less than or equal to 0.5 mm, whereby thermal stress due to a difference in thermal expansion between the tip and the electrode base material can be reduced. A total of continuous distances of the welded portions on the joining surface, are 0.4 times to 0.8 times a length from an end of the tip to another end thereof, whereby joining strength of the welded portion can be assured. Peeling at the tip or falling-off of the tip due to thermal stress can be less likely to occur, whereby durability of the ground electrode can be improved.

A metal shell for a spark plug is made from a steel material that has increased carbon content and, in some embodiments, boron as well. The steel material is well-suited for extrusion because of its ductility, while maintaining requisite strength. The spark plug shell may have a reduced outer diameter (OD.sub.HL) at a crimped hot lock region, such as the case when the shell is used in smaller diameter spark plugs, such as M8 and M10 plugs. According to a non-limiting example, the spark plug shell steel material comprises 0.20-0.55 wt % carbon, inclusive.

A spark plug is provided with a center electrode and a ground electrode. The ground electrode includes an electrode tip, an electrode base material, an intermediate member and a first melt portion. The intermediate member is disposed between the electrode tip and the electrode base material. The first melt portion contains components of the electrode base material and the intermediate member, and is disposed at least at a part of the boundary between the electrode base material and the intermediate member. In a cross section including the axis of the ground electrode, the boundary line between the intermediate member and the first melt portion has at least two first projection portions projecting toward the electrode tip side, and the boundary line between the electrode base material and the first melt portion has at least two second projection portions projecting toward the opposite side of the first projection portions.

A spark plug electrode with an electrode tip formed on an electrode base using an additive manufacturing process, such as a powder bed fusion technique. The spark plug electrode includes an electrode base, an electrode tip that is formed on the electrode base and includes a precious metal-based material, and a thermally resilient joint that is located between the electrode base and the electrode tip, wherein the electrode tip and the thermally resilient joint together include a number of laser deposition layers.

A spark plug electrode with an electrode tip formed on an electrode base using an additive manufacturing process, such as a powder bed fusion technique. The spark plug electrode includes an electrode base, an electrode tip that is formed on the electrode base and includes a precious metal-based material, and a thermally resilient joint that is located between the electrode base and the electrode tip, wherein the electrode tip and the thermally resilient joint together include a number of laser deposition layers.

A spark plug having a center electrode, a ground electrode, and a noble metal tip that is joined to a part of the ground electrode near one end of the ground electrode via a fused portion. The fused portion extends outward beyond an outer shape of the noble metal tip so that a part of the fused portion is present at each of positions that are located inward from and separated from both side edges of the ground electrode in a width direction of the ground electrode. The fused portion includes a fused protrusion that is located near at least one of two side edges of the noble metal tip in the width direction of the ground electrode and that protrudes in a direction away from the one end of the ground electrode.

A spark plug having a center electrode, a ground electrode, and a noble metal tip that is joined to a part of the ground electrode near one end of the ground electrode via a fused portion. The fused portion extends outward beyond an outer shape of the noble metal tip so that a part of the fused portion is present at each of positions that are located inward from and separated from both side edges of the ground electrode in a width direction of the ground electrode. The fused portion includes a fused protrusion that is located near at least one of two side edges of the noble metal tip in the width direction of the ground electrode and that protrudes in a direction away from the one end of the ground electrode.

An electrode material for at least one of a center electrode (5) and a ground electrode (27) provided with a chip (31, 32) for use in a spark plug (1). The electrode material contains Ni as a principal component, and has a Si content of from 0.50% to 1.0% by mass, an Al content of from 0.2% to 2.0% by mass, a Cr content of from 12% to 34% by mass, a rare-earth element or the like content of from 0.03% to 0.2% by mass, a Fe content of more than 0% but not more than 20% by mass, a C content of not more than 0.10% by mass, and a Mn content of not more than 1.0% by mass. The total content of Si and Al is not less than 0.80% by mass, and less than one tenth of the Cr content.

An electrode material for at least one of a center electrode (5) and a ground electrode (27) provided with a chip (31, 32) for use in a spark plug (1). The electrode material contains Ni as a principal component, and has a Si content of from 0.50% to 1.0% by mass, an Al content of from 0.2% to 2.0% by mass, a Cr content of from 12% to 34% by mass, a rare-earth element or the like content of from 0.03% to 0.2% by mass, a Fe content of more than 0% but not more than 20% by mass, a C content of not more than 0.10% by mass, and a Mn content of not more than 1.0% by mass. The total content of Si and Al is not less than 0.80% by mass, and less than one tenth of the Cr content.

A spark plug electrode having greater mechanical stability. The spark plug electrode includes a base body and a noble metal pin situated on the base body, the base body and the noble metal pin being connected to each other by a connection zone. The connection zone has at least one first welding seam and one second welding seam.