Manufacturing pistons

A method of manufacturing a piston for use in an internal combustion engine, the method comprising forming a blank (10;

• 50;
• 70) from a first material, the blank being arranged to form at least a crown portion (10a;
• 50a;
• 70a) of the piston and having a surface portion (12;
• 52;
• 54) arranged to define at least one recess, (14;
• 28;
• 56;
• 68;
• 86) the method also comprising providing a region of a second material (20;
• 60;
• 80) in said surface portion, the second material being secured to said first material, the method also comprising forming the recess in said surface portion so that the recess has a bounding surface (14a;
• 56a;
• 86a) at least part of which is formed by the second material, characterised in that said region of the second material is formed and secured to the first material by inserting a tool (22) into the blank, bringing about relative reciprocating movement between the tool and the blank so that frictional heat is generated plasticising the material adjacent to the tool, and by causing relative translational movement between the blank and the tool while continuing the reciprocating movement therebetween so that the tool moves through said region of the blank, thereby forming the second material and mixing it with the first material at the edges of said region to secure the materials together: