Solid state welding processes

Solid-State Welding. Sohd-state welding comprises a group of welding processes wherein a bond is made between two base materials upon the apphcation of pressure at a temperature below the soHdus of the base materials (Table 1). Interlayers are sometimes used. By joining materials in the sohd state, many of the difficulties of the fusion processes are avoided. 

General Description. Adhesive wear is defined as wear by transference of material from one surface to another during relative motion under load due to a process of solid-state welding (Fig. 16) particles that are removed from one surface are either permanently or temporarily attached to the other surface. 

The exposed pads on the chip top-level passivation windows are connected to fingers on the metallic lead frame with fine 25-pm Au or A1 wire (Cu or Ag is sometimes also used) by a solid-state wirebonding process using thermocompression and/or ultrasonic welding [9,10]. The lead frame, which also forms the external, board-level interconnects, is usually made from an Ni-Fe alloy, Cu alloy, or Cu-clad stainless steel. As with discrete connectors, the bare frame is usually given an Ni or Ni-Co strike and then plated with Au, Ag, or Pd for improved corrosion resistance and reduced contact resistance [9]. 

Friction welding is the most common solid-state process. One type, direct-drive friction welding, is accomplished by spinning one piece rapidly against a second, stationary piece to produce frictional heating. When the metal is at a forging temperature below the solidus, rotation is stopped and axial force is applied. Heated metal, together with oxide and surface contamination, is squeezed out of the interface between the two pieces in the form of a metal flash, which can be trimmed to form a smooth surface. 

Stationary systems based on CO2 lasers and robot-controlled systems using solid-state lasers have been introduced into the industrial marketplace. Remote laser welding is the latest in a series of successful industrial laser solutions that have revolutionized sheet metal processing over the past 30 years. 

Friction Welding Processes Friction forces work decaying into heat can be used in order to reach the solid-state IxMiding of metals. Actually three different operations are usually considered as described in the following. 

As a result of this process, a joint is produced in solid state. Because of various geometrical features of the tool, the material movement around the pin can be quite complex. During FSW process, the material undergoes intense plastic deformation at elevated temperature, resulting in generation of line and equiaxed recrystallized grains. The fine microstructure in friction-stir welds produces good mechanical properties of the joints, both static and dynamic. 

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