Bert Liu

Depiction of interfacial morphology in impact welded Ti/Cu bimetallic systems using smoothed particle hydrodynamics

Numerical simulations of high-velocity impact welding are extremely challenging due to the coupled physics and highly dynamic nature of the process. Thus, conventional mesh-based numerical methodologies are not able to accurately model the process owing to the excessive mesh distortion close to the interface of two welded materials. A simulation platform was developed using smoothed particle hydrodynamics, implemented in a parallel architecture on a supercomputer. Then, the numerical simulations were compared to experimental tests conducted by vaporizing foil actuator welding. The close correspondence of the experiment and modeling in terms of interface characteristics allows the prediction of local temperature and strain distributions, which are not easily measured.

Impact Welding Structural Aluminium Alloys to High Strength Steels Using Vaporizing Foil Actuator

Dissimilar Al/Fe joining was achieved using vaporizing foil actuator welding. Flyer velocities up to 727 m/s were reached using 10 kJ input energy. Four Al/Fe combinations involving AA5052, AA6111-T4, JAC980, and JSC1500 were examined. Weld samples were mechanically tested in lap-shear in three conditions: as-welded, corrosion-tested with ecoating, and corrosion-tested without coating. In all three conditions, the majority of the samples failed in the base aluminium instead of the weld. This shows that the weld was stronger than at least one of the base materials, both before and after corrosion testing. Galvanic corrosion was not significant since the differences in open cell potential, which represent the driving forces for galvanic corrosion, were small among these materials—no more than 60 mV in all cases. Nonetheless, through corrosion testing, the base materials suffered general corrosion, which accounted for the weakening of the base materials.

Use of Vaporizing Foil Actuator for Impact Welding of Aluminum Alloy Sheets with Steel and Magnesium Alloys

The vaporizing foil actuator (VFA) is a novel tool for impulse-based metal working operations. In this work, it has been used for impact welding of aluminum flyer sheets to high-strength steel and magnesium plates. Aluminum alloy 6061 sheets of 0.81 mm thickness were launched to velocities in excess of 800m/s and found to weld to both the target materials investigated: HSLA A588 steel and AM60B magnesium alloy. Grooved as well as flat target plates were utilized. Welding with grooved target plates was found to be not very robust as the weld samples came apart during sectioning. However, the flat targets welded successfully, and during mechanical testing, failure was found to occur outside the joint. The weld interface morphology for each material system and configuration has been shown. Some improvements to the grooved-target experimental configuration are also demonstrated.

Solid State Impact Welds Between Dissimilar Metals Utilizing Vaporizing Foil Actuators: A Microstructural Evaluation

This work aims to study the effect of microstructures of collision welds between various dissimilar metals on the mechanical properties of the weld. In this work, welding between the aluminum-copper, copper-titanium, aluminum-magnesium, titanium-steel, and copper-steel was attempted, and the weld interfaces were examined using optical and electron microscopy. Instrumented peel tests were performed for a qualitative correlation of weld strengths and weld interface microstructure.

Vaporizing Foil Actuator Welding of AA6061 With Cu110: Effect of Heat Treatment Cycles on Mechanical Properties and Microstructure

This work aims to study the effect of microstructure of the weld between aluminum alloy AA6061 and commercially pure copper, Cu 110, on its mechanical properties. AA6061-T6 and T4 aluminum sheets of 1 mm thickness were launched towards copper targets using the Vaporizing Foil Actuator (VFA) tool operating at 8 kJ input energy level. Flyer plate velocities, measured via photonic Doppler velocimetry (PDV), were observed to be approximately 800 m/s. All the welded samples were subjected to instrumented peel testing, microhardness testing, energy-dispersive x-ray spectroscopy (EDS), and SEM. The welded joints had cracks which ran through the continuous intermetallic layers and stopped upon encountering a ductile metallic wave. The welds created with T6 temper flyer sheets were found to have smaller regions with wavy interfaces free of intermetallics as compared to those created with T4 temper flyer sheets. Peel strength tests of the two types of welds resulted in failure along the interface in case of the T6 flyer welds, while the failure generally occurred in the parent aluminum in the case of the T4 flyer welds. Half of the T4 flyer welds were subjected to aging for 18 hours at 160 °C to convert the aluminum sheet back to T6 condition. Although the flyer material did not attain the hardness of the original T6 material, it was found to be significantly stronger than the T4 material. These welds retained their strengths after the aging process and diffusion across the interface was insignificant.Copyright