Mechanical properties and macrostructure of dissimilar friction stir welding of aluminum alloys

Welding of dissimilar aluminum alloys (AA) is not reliable by using fusion welding techniques. Many fusion defects such as porosity and hot crack have been observed by these techniques due to the melting of these alloys. It can eliminate the fusion defects by using a different process technique to join these alloys without melting. One of this processes is friction stir welding. This process is a solid state joining technique which joins metals under its melting temperatures. This process uses a tool which consists a shoulder to produce heat by friction and a pin to stir the welded metals. The most aluminum alloys have common applications are 5xxx and 6xxx aluminum series. This paper investigates the effects of FSW variables on mechanical properties and macrostructure of a dissimilar welding between one of 5xxx aluminum series (AA5454 ) and one of 6xxx aluminum series (AA6061-O annealed temper). 26 joints were welded with different variable conditions to use in this investigation. Tensile test and micro hardness measurements were used to evaluate the mechanical properties. An optical microscope was used to examine different weld zones. Process variables used in this investigation are rotational speed, traverse speed, and tool design. The values of the rotational speeds and the traverse speeds used in this study are 1000, 1225, 1550 rpm and 17, 21, 42.5, 67.5, 13, 210 mm/min, respectively. Two tools with different dimensions were used. The maximum tensile strength of the welded joint achieved is 125Mpa. It is approximately equal to the strength of the AA6061 base metal. The best process variables values are 1225 rpm rotational speed and 17mm/min traverse speed. The macrostructure analyses show that the higher the diameter ratio between the shoulder and the pin of the tool, the better the stirring of the metal in the weld zone.