a welding apparatus is provided for forming a weld joint between first and second elements of a workpiece . the apparatus heats the first and second elements to form an interface of material in a plasticized or melted state interface between the elements . the interface material is then allowed to cool to a plasticized state if previously in a melted state . the interface material , while in the plasticized state , is then mixed , for example , using a grinding / extruding mixer , to remove any dendritic - type weld microstructures introduced into the interface material during heating .