Compound connection mechanism of Al2O3 ceramic and TC4 Ti alloy with different joining modes

In this paper, laser welding-brazing of TC4 Titanium (Ti) alloy and Al2O3 ceramic dissimilar material was carried. The results showed that the Ti alloy and Al2O3 were joined by melting filler metal when the laser was concentrated in the Ti alloy side of the joint. The joint with one fusion weld and one brazed weld separated by remaining unmelted Ti alloy. Laser beam offset the Ti alloy 1.5 mm, Ti alloy would not be completely melted in joint. Through heat conduction, the filler metal melted occurred at the Ti-ceramic interface. A brazed weld was formed at the Ti-ceramic interface with the main microstructure of β-CuZn + Ti2Zn3, β-CuZn and Al2Cu + β-CuZn. The joint fractured at the brazed weld with the maximum tensile strength of 169 MPa.

Remanufacturing the AA5052 GTAW Welds Using Friction Stir Processing

Progress in sustainable manufacturing is a crucial element to minimise negative environmental impacts. The conventional fusion weld process used to join aluminium alloys resulted in coarse grain structure, inevitable defects, and severe joint softening. Friction stir processing (FSP) has the potential to modify the microstructure of materials in joint structure and improve the mechanical properties. In this investigation, the effect of friction stir post–processing was evaluated to study the microstructural characteristics and mechanical properties of GTAW (gas tungsten arc welding) welds in the aluminium 5052 alloy. During FSP, the grains’ dendritic microstructure was destroyed, and the dynamic recrystallisation resulted in a very fine and equiaxed grains structure in the fusion zone. The hardness of the friction-stir-processed welds significantly improved because of microstructure grain refinement. The processed joint demonstrated higher ultimate tensile and yield strength (~275 MPa and 221 MPa, respectively) and superior elongation (31.1%) compared to the unprocessed weld; at the same time, the mechanical strength (yield and ultimate tensile) is similar to that of the base metal.

Microstructure and mechanical property improvement of dissimilar metal joints for TC4 Ti alloy to Nitinol NiTi alloy by laser welding

To avoid the formation of Ti-Ni intermetallics in a joint, three laser welding processes for Ti alloy–NiTi alloy joints were introduced. Sample A was formed while a laser acted at the Ti alloy–NiTi alloy interface, and the joint fractured along the weld centre line immediately after welding without filler metal. Sample B was formed while the laser acted on a Cu interlayer. The average tensile strength of sample B was 216 MPa. Sample C was formed while the laser acted 1.2 mm on the Ti alloy side. The one-pass welding process involved the creation of a joint with one fusion weld and one diffusion weld separated by the remaining unmelted Ti alloy. The mechanical performance of sample C was determined by the diffusion weld formed at the Ti alloy–NiTi alloy interface with a tensile strength of 256 MPa.

Laser welding-brazing of alumina to 304 stainless steel with an Ag-based filler material

In this paper, laser welding-brazing of 304 stainless steel (SS) and Al2O3 ceramic dissimilar metal material was carried out. The results showed that the SS and Al2O3 were joined by melting filler metal when the laser was focused on the SS side of the joint. One process was one pass welding involving creation of a joint with one fusion weld and one brazed weld separated by remaining unmelted SS. When laser beam was focused on the SS plate 1.5 mm, SS would not be completely melted in joint. Through heat conduction, the filler metal (68.8 wt.% Ag, 26.7 wt.% Cu, 4.5 wt.% Ti) melting occurred at the SS-Al2O3 ceramic interface. A brazed weld was formed at the SS-Al2O3 ceramic interface with the main microstructure of Cu[s.s.] + Ag[s.s.], Ti2Cu + TiFe and Ag + AlCu2Ti. The joint fractured in reaction layer at the ceramic side with the maximum tensile strength of 74 MPa.

Investigation of Thermal Conditions of the Aluminothermic Welding and their Influence on the Structure and Properties of Metal Rails

Rail welded joints are integral part of continuous welded rail. However, they often do not have sufficient reliability during the operation. The article is devoted to the assessment of temperature influence effect on the mechanical properties and structure of weld metal and welded rails. The temperature distribution across the rail section in welded zone during the cooling process of aluminothermic rail welding is obtained using simulation by LVMFlow. The results of the study of hardness and structure of metal rail aluminotermitic welded joints are given. It is shown that the hardness of rail welded joints increases from 24 HRC to 38 HRC in the fusion zone of the weld metal and rail metal. It is due to the harmful effects of overheating of the metal during the welding process. The hardness is confirmed by microstructural analysis. Microstructural analysis showed the differences in the grains sizes of metal welded zone and heat affected zone. The structure of welded metal is acicular dendritic. Owing to a difference between structures of the welded joint zones the probability of occurrence of cracks on the boundary of fusion weld and metal is increased.