Influence of tool rotational speed on the evolution of microstructure and mechanical properties of precipitation-hardened Aluminium 6061 butt joint during friction stir welding

The present investigation intends to interpret the effect of tool rotational speed on the mechanical properties and microstructural evolution in Aluminium 6061-T6 alloy during friction stir welding. A higher value of tool rotation produces more hardness at the nugget zone, which is attributed to the higher intensity of reprecipitation at higher rpm, revealed by transmission electron microscopy. The nugget zone is revealed as a nearly precipitate-free region, while the thermo-mechanically affected zone contains coarse precipitates, deformed and dynamically recovered grains with a few recrystallized grains. Significant reduction in grain size in the stirred zone is also a key finding. The observations depict the dependence of microstructure, and thus mechanical behaviour on tool rotational speed. A specific combination of process parameters has been determined from experiments, which corresponds to the maximum joint efficiency.

Effect of Coating and Welding Wire Composition on AHSS GMA Welds

Advanced high-strength steels (AHSS) such as complexphase (CP) and high-formability (HF) steel offer weightsaving advantages for automotive applications such as chassis and frame applications. To prevent material oxidation, materials are often galvanized to protect the substrate from corrosion. However, the weldability of coated AHSS becomes challenging due to the trapping of zinc in the weld molten pool, which could lead to weld defects such as porosity and liquid metal embrittlement cracks. This work focused on the weldability of AHSS (CP800 and 980HF) using the gas metal arc welding process. The roles of both galvanized iron coating and filler material on weld strength were investigated. The welds were performed using two different filler materials: a low-strength filler (ER70S-6) and a high-strength filler (ER100S-6) material. In addition, two different joint configurations were studied: lap joints and butt joints. The results showed that the butt joint had a higher strength compared to the lap joints. Furthermore, the strength of the butt joint overmatched the base material strength in all of the tested materials (both in galvanized and uncoated). In general, lap joint strength undermatched the base material strength, which was attributed to the rotation during tensile testing that induced unaccounted bending stress on the lap joint, while using a higherstrength welding wire improved the tensile strength material in the lap joint configuration. The hardness profiles in the 980HF steel also showed a significant hardness mismatch due to the formation of a fully martensitic microstructure in the heat-affected zone, which led to suppressing the deformation across the lap joint.

Temperature Field in MIG Welding of Thin Plate of Stainless Steel

This paper studies the butt welded joint of SUS316L stainless steel. The butt joint is not beveled, has a gap and is welded in one pass by MIG welding process. First, the welding parameters of this weld are determined through calculation and test welding for the butt joint of two plates of 3 mm in thickness. Then these welding parameters are used as input data to calculate and determine the temperature field by two methods: the calculation method based on the theory of heat transfer process and the numerical simulation method of welding processes that relies on SYSWELD software on the basis of the finite element method. The calculation results of the two methods were compared with each other and tested by experiment to show the reliability of calculation and simulation results.

InP based high speed p-i-n photodetector monolithic integrated with MQW semiconductor optical amplifier

We demonstrate an InP based high speed p-i-n photodetector monolithic integrated with MQW semiconductor optical amplifier. A butt-joint scheme is adopted to connect the SOA and evanescent wave photodetector. The chip allows separate design for SOA and PD and needs only two MOCVD growth steps, which promises high yield and reduced manufacturing cost. The fabricated 5×20 μm2 PD shows a low dark current of 300 pA at -3V. The optical gain bandwidth of the SOA is 50nm, covering whole c-band. Gain ripple of SOA is 0.5dB, indicating that internal parasitic reflectivity is negligible. For integrated chip with 500μm SOA, the on-chip gain and total chip responsivity at 1545 nm can reach 12.8 dB and 7.8 A/W respectively. Insertion loss of the butt-joint interface is estimated to be 1.05 dB/interface. Small signal 3dB bandwidth at -5V of the integrated chip reaches 20GHz, showing no deterioration compared to discrete PD.