<p class="Abstract"><span lang="EN-GB">Friction welding is a welding technique that utilizes heat due to surface friction between a rotating and pressing workpiece. This study aims to analyze the effect of environmental temperature variations on the mechanical properties of Al 6061 alloys, friction welding specimens with variations in room temperature (27ºC), 50 ºC, 75 ºC, 100 ºC, 125 ºC, and 150 ºC. Welding is carried out using a lathe with a rotation speed of 1600 rpm, a workpiece diameter of 15 mm, a champer angle of 15º, a friction force of 65 bar for 6 seconds, and a final compressive force of 325 bar for 60 seconds. Changes in mechanical properties in terms of tensile strength and hardness. The results showed that the higher working environment temperature produced greater tensile strength than Al 6061 friction weld joints. From macro-micro observations, it was found that specimens with large tensile strength (specimens welded at 100 ºC, 125 ºC, and 150 ºC) had a large area (Zpl) and finer granules when compared to specimens with small tensile strength (specimens welded at room temperature (27 ºC), 50 ºC and 75 ºC).</span></p>

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Rotary Friction Welding is a solution in addressing the poblems in welding of material difficult to weld by fusion welding, such as AA6061 aluminium alloy. Fusion welding is difficult to apply to aluminium alloy because of porosity and crack which often occur during solidification. From the research on friction welding of AA6061, it can be conclude that excessive welding temperature of friction welding may result in thermal softening in weld zone and HAZ. The excessive cooling rate after friction welding run will affect to formation of hard and brittle of weld zone. Increase of environmental temperature above room temperature will accelerate workpiece to achieve solid state condition and lowering difference between weld peak temperature and inital weld temperature (ΔT) which mean decreasing of coooling rate. In this research, environmental temperature were varied of 27 °C (room temperature), 50 °C, 75 °C, 100 °C, 125 °C dan 150 °C. Some parameters are set constant such as rotation speed of 1600 rpm, friction pressure of 65 bar or 65 kg.cm−2, friction time (tf) of 6 seconds, forging pressure of 325 bar or 325 kg.cm−2, forging time of 60 seconds, contact diameter of workpiece of 15 mm and the workpiece chamfer angle of 15°. The contact area is divided into three zones, which are the plastic deformation zone (Zpl), the partial deformation zone (Zpd) and the non-deformed zone (Zud). The higher the environmental temperature will produces the wider plastic zone and plastic deformation zone (Zpl + Zpd). The higher the environmental temperature will causes the yield strength of the AA 6061 friction weld joint to increase which modelled as y = 3E-05x2 + 0.0033x + 16.582. Likewise, the tensile strength of the AA 6061 friction weld joint also increases which modelled as y = 3E-05x2 + 0.0026x + 18.119. When comparing the hardness of rotating workpiece side (spin) with workpiece side pressing (press), the previous one is higher at all variations of the temperature. From the photograph of the microstructure of base metal of Al 6061, dark particles (Mg2Si) and gray particles (Fe3SiAl12) are present in the Al matrix. The grain structure of Zud is bigger than Zpd and Zpl. Zpd microstructures at all environmental temperatures form smaller granular structures than base metal grains. Zpl microstructure in workpieces with environmental temperature of 27 °C, 50 °C, 75 °C and 100 °C were formed in small granular structure with Mg2Si (black) and Fe3SiAl12 (gray) structure which spread evenly. However Zpl microstructure with environmental temperature of 125 °C and 150 °C seems to enlarge, especially the structure of Fe3SiAl12 (gray), due to overheat and excessive softening.

Aluminum alloy is non-Ferro material that very difficult to amalgamate using fusion welding, so it requires friction method. Friction welding is process for connecting metals without melting (solid state process), Process merging between the rotating speeds of material forces cause heat friction and at somepoint can be able to melt the materials and melting process occurs. The study aim is to determine tensile strength results from friction weld joints due to changes in ambient temperature of room. Material test is Aluminum A6061. Friction welding uses a lathe with rotation speed of 1600 rpm. The length size of material is 80 mm and 120 mm, diameter 15 mm, Champer angle 15°, 65 bar friction force for 60 seconds, final compressive force 375 bar for 60 seconds and variations in ambient temperature namely room temperature (T 0),125 °C ,150°C. The A 6061 joint produces the highest tensile strength at temperature 150 o C (188 MPa).

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