Grain Size in Aluminum Alloy 6061 under Hot Ring Compression Test and after T6 Temper

Peripheral coarse grain during and after hot forming is often a major inconvenience for manufacturing aluminum alloy parts. Not only is the strength reduced, but the subsequent surface treatments are also hard to realize. The literature has shown that peripheral coarse grain is very likely induced by the previous process, such as extrusion. To investigate if peripheral coarse grain could be caused solely by hot forming, this study removed the billet surface layers. This eliminates the effect from the previous processes preparing the billets and forms ring specimens for executing ring compression test. The ring compression test can reveal the friction circumstance of the specimen to the die surface and create versatile deformation in the specimens to simulate forging situations, thereby providing multifaceted conditions to develop diverse grain size in specimen, particularly on its surface. The experiments were designed and analyzed under the Taguchi method, with consideration for factors such as working temperature, speed and amount of compression, and lubricant. Under each experiment, no peripheral coarse grains were found in the specimen, which were peeled and compressed, and even the average grain size after compression test is larger than that of the received billet. No peripheral coarse grains were found in the subsequent T6 temper either, which could, however, refine the grains.