Homogeneity of Mechanical Properties of Underwater
Friction Stir Welded 2219-T6 Aluminum Alloy
یکنواختی خواص مکانیکی جوشکاری آلیاژ آلومینیوم 2219-T6
جوشکاری اصطکاکی اغتشاشی شده درزیر آب
ABSTRACT
Underwater friction stir welding (FSW) has been demonstrated to be available for the improvement in tensile strength of normal FSW joints. In order to illuminate the intrinsic reason for strength improvement through underwater FSW, a 2219 aluminum alloy was underwater friction stir welded and the homogeneity of mechanical properties of the joint was investigated by dividing the joint into three layers. The results indicate that the tensile strength of the three layers of the joint is all improved by underwater FSW, furthermore, the middle and lower layers have larger extent of strength improvement than the upper layer, leading to an increase in the homogeneity of mechanical properties of the joint. The minimum hardness value of each layer, especially the middle and lower layers, is improved under the integral water cooling effect, which is the intrinsic reason for the strength improvement of underwater joint.
Features of AcousticEmission Signals during the Initiation
of a Fatigue Failure in a Welded Joint of an Aluminum Alloy
of the Al–Cu–Mn System
ویژگی های سیگنال انتشار آکوستیک در طول شروع یک شکست خستگی
در یک اتصال جوش داده شده آلیاژ آلومینیوم سیستم Al-Cu-Mn
ABSTRACT
The features of the generation of acoustic emissions (AEs) during the initiation of a fatigue failure in various zones of a welded joint of thermally hardened 2219T6grade aluminum alloy, which is produced using electronbeam welding, are considered. Metallographic studies showed that a welded joint of the alloy is structurally and mechanically inhomogeneous. This predominantly influ ences the initiation and development kinetics of fatigue cracks in the joint and the AE kinetics. It is shown that the area of a formed flaw is proportional to the sum of the amplitude of detected signals, and the transition from the initiation to the stable propagation of a failure is accompanied by an abrupt increase in AE activity.
اتصال آلومینیوم و منیزیم از طریق جوشکاریA-TIG
با پیش نورد کمکی همراه با لایه میانی روی
ABSTRACT
AZ31B Mg and 6061 Al alloys were successfully welded via a novel pre-roll-assisted A-TIG welding technique with Zn interlayer at an overlap configuration. The rolling operation increased the contact area and control tightly between Zn interlayer and plates at an interlayer-assisted overlap configuration to avoid the adverse effect of gaps. B2O3 activating flux was coated on the upper Al plates to provide contraction of the arc column to increase the arc energy density; welding penetration was increased without improving heat input, which reduced the formation and grain coarsening of Al–Mg IMCs. Therefore, the tensile–shear strength of the joints was improved obviously. The average of tensile–shear strength joined was 71.2 MPa with a maximum of 74 MPa compared to 41.1 MPa with a maximum of 45.2 MPa by conventional TIG with Zn interlayer.
Effect of welding parameters on the solidification microstructure
of autogenous TIG welds in an Al–Cu–Mg–Mn alloy
تاثیر پارامترهای جوشکاری بر میکروساختار انجمادی جوش های TIG
بدون ماده پر کننده در یک آلیاژ Al–Cu–Mg–Mn
ABSTRACT
The weld metal microstructures of autogenous TIG welds have been investigated for a range of welding conditions using an Al–Cu–Mg–Mn alloy. It was found that a combination of high welding speeds and low power densities provide the thermal conditions required for the nucleation and growth of equiaxed grains in the weld pool, providing heterogeneous nucleation sites are available. The most likely origin of the nucleants is from a combination of dendrite fragments and TiB2 particles that survive in the weld pool. The finest microstructure was observed in the centre of the weld and is attributed to the higher cooling rates which operate along the weld centreline. Composition profiles across the dendrite side arms were measured in the TEM and were found to follow a Scheil type segregation behaviour where there is negligible back diffusion in the solid. The measured core concentration of the dendrite side arms was found to rise with increasing welding speed and was attributed to the formation of significant undercoolings ahead of the primary dendrite tip, which enriched the liquid surrounding the dendrite side arms.