Physical simulation of microstructural evolution in linear friction welded joints of Ti–6Al–4V alloy

Abstract

The novel shear compression specimen was used to simulate the microstructural evolution in linear friction welding joints of Ti–6Al–4V alloy. Similar formation mechanisms of microstructures and microtextures were found in the linear friction welding joints and shear compression specimen. Accordingly, the shear compression test was proved to simulate the microstructural evolution and the thermomechanical conditions that occurred in linear friction welding joint. Furthermore, the strain rate in linear friction welding was estimated to exceed the value of 70?s^??1.     

Influence of Mn on microstructural evolution in Ti-killed C–Mn steel

The influence of manganese on the microstructure in C–Mn steels containing a small amount of titanium oxide particles as inoculants for acicular ferrite during the austenite–ferrite transformation has been studied. An acicular ferrite dominant microstructure could be produced when the Mn concentration is larger than about 2 wt.%.     

Microstructures and mechanical properties of friction stir welded joints of Zr–Ti alloy

Zirconium–titanium alloy joints were successfully produced by friction stir welding. Unlike the (α+β) dual phase microstructure in base metal, only the β phase existed in the region in which temperature exceeded the β transient point for the as welded joint. Accordingly, the hardness in these regions exhibited integral decrement and uniform distribution features. The thermal simulation further showed that hardness variation was mainly determined by phase composition. Microstructure development in the nugget zone was mainly governed by continuous dynamic recrystallisation. Satisfactory ultimate tensile strength and elongation equal to the base metal were achieved in the as welded joint. Tensile fracture occurred at the heat affected zone near the retreating side of the joint. The fracture surface of the joint exhibited a mixing feature with quasi-cleavage facets and small dimples.     

Effect of microstructural heterogeneities on scatter of toughness in multi-pass weld metal of C–Mn steels

Often, scatter in mechanical properties of multi-pass steel weldments is qualitatively attributed to the underlying heterogeneous microstructure brought about by spatial variations of multiple thermal cycles. In this research, a method for quantitative heterogeneity calculation based on measured variations of microstructure and hardness throughout the multi-pass weld metals including various reheated regions was explored. Published data from multi-pass welds with controlled titanium additions (7–32 wt ppm) were correlated to comprehensive microstructure characterization. The scatter in 7 wt ppm Ti steel welds was larger than that of 32 wt ppm Ti steel welds. This change in scatter is correlated to spatial distributions of microstructural heterogeneity parameter, rather than the average value of heterogeneity parameter for the whole weldment.     

Mechanical properties of friction stir welded armor grade Al–Zn–Mg alloy joints

The influence of different welding speeds and rotary speeds on the formation and mechanical properties of friction stir weld joints of armor grade aluminum alloy was presented. The developed weld joints were characterized by bend tests, micro-hardness tests, tensile tests, optical and scanning electron microscopies. Mechanical properties (i.e., micro-hardness, ultimate tensile strength and elongation to fracture) increased with the increase in rotary speed or decrease in welding speed. The effect of welding speed on micro-hardness of heat affected zones was more profound than the rotary speeds. The welding speeds and rotary speeds influenced the mechanical properties and their effects on various mechanical properties of the friction stir welded joints can be predicted with the help of regression models.     

Bending properties of friction stir welded joints – Studies on characteristics of friction stir welded joints in structural aluminum alloys (report 4)

The objective of this work is to determine the best parameters for brazing ceramic joints of pre-metallized Al₂O₃ with Ti by a plasma process using amorphous ribbons of Cu₄₉Ag₄₅Ce_x alloy as the addition metal. The alloys were prepared in an arc oven, and later processed by melt spinning, varying Cerium content by 4–6%. Brazing took place in a vacuum oven and the following variables were analysed: deposition time of the Ti film and temperature and brazing time, which were related to the flex resistance in three points of the brazed joint. A linear regression equation was obtained, and the interaction between these factors was verified. The metallized ceramic surfaces showed excellent uniformity and the brazed joints demonstrated very good adhesion, achieving flex resistance values of up to176.8 MPa.     

Effect of the surface roughness of friction stir welded joints on the fatigue characteristics of welded joints in V-1461 and V-1469 aluminium–lithium alloys

Investigations were carried out into the effect of friction stir welding conditions of V-1461 and V-1469 aluminium–lithium alloys on surface roughness and mechanical properties of welded joints. The general parameter of the welding conditions was the heat input coefficient determined by the ratio of the speed of rotation of the tool to the welding speed. The optimum range of friction stir welding conditions of sheets of the investigated alloys was determined. In this stage, the surface finish of the welded joint after welding is much better (required for increasing the fatigue characteristics and high-quality deposition of protective coatings), there are no defects and the strength of the welded joint is equal to 0.75–0.85 of the strength of the parent material. The production of the welded joints with reduced surface roughness (R_z ≤ 40 μm) greatly increases the fatigue characteristics of the welded joints (low-cycle fatigue strength equals more than 300,000 cycles without fracture).     

Microstructural characteristics and mechanical properties of Al–Mg–Si alloy self-reacting friction stir welded joints

The 5?mm thick Al–Mg–Si alloy was self-reacting friction stir welded using the specially designed tool at a constant rotation speed of 400?rev?min^?1 with various welding speeds. Defect-free welds were successfully obtained with welding speeds ranging from 150 to 350?mm?min^?1, while pore defects were formed in the weld nugget zone (WNZ) at a welding speed of 450?mm?min^?1. Band patterns were observed at the advancing side of WNZ. Grain size and distribution of the precipitated phase in different regions of the joints varied depending on the welding speed. The hardness of the weld was obviously lower than that of the base metal, and the lowest hardness location was in the heat affected zone (HAZ). Results of transverse tensile tests indicated that the defective joint fractured in the WNZ with the lowest tensile strength, while the fracture location of the defect-free joints changed to the HAZ.     

Mechanical properties of friction stir welded joints of 1050 – H24 aluminium alloy

Abstract

The friction stir welding (FSW) of 1050 - H24 aluminium alloy was performed to investigate the mechanical properties of the joints and determine the optimum FSW parameters. The mechanical properties of the joints were evaluated via tensile tests. The experimental results showed that a distinct softened region located at the weld and heat affected zones occurred in the joints. The degree of softening and tensile properties of the joints are significantly affected by the welding process parameters, such as welding speed and rotation speed. The optimum FSW parameters can be determined from the relations between the tensile properties and the welding parameters, and the maximum tensile strength of the joints is equivalent to 80% of that of the base material. When the welding parameters deviate from the optimum values, a crack like defect or significant softening is produced in the joints, thus the tensile properties of the joints deteriorate and the fracture locations of the joints change. All these results can be explained by the hardness distributions and welding defects in the joints.     

Tensile properties and mechanical heterogeneity of friction stir welded joints of 2014 aluminum alloy

1 INTRODUCTIONFriction stir welding ( FSW) is a new andpromising welding process that can produce low-cost and high-quality joints of many alloys[1 7]becauseit does not need consumable filler materialsand can eli minate some welding defects such ascrack and porosity . In the FSW process , thewelding temperature is lower than that in thefusion welding, and the metal is in the plasticstate ,so many fusion welding defects can be avoi-ded. At present , more and more researches havebeen focu…     

Improvement of impact strength of friction‐welded joints by weld interface shape optimisation

The theoretical and practical principles of heat, thermomechanical treatment and textural hardening of weldable titanium alloys are described. The results of investigations of the effect of deformation and heat treatment on the mechanical properties of welded joints in titanium alloys are presented.     

Properties of as welded and heat treated pure titanium–7075 Al–Zn–Mg alloy friction weld joints

Abstract

The effects of joining conditions and an age hardening post­weld heat treatment (PWHT) at 120°C for 24 h on the tensile strength and metallurgical properties of dissimilar friction joints between pure titanium and age strengthened 7075 Al–Zn–Mg alloy were investigated. Highest strength was achieved using intermediate friction pressure (150 MPa), short friction time (0.5 s), and high upsetting (forging) pressure (400 MPa). The joint tensile strength decreased when the joint diameter was increased from 8 to 16 mm. The joint tensile strength of as welded (AW) dissimilar joints was similar to that of PWHT joints with diameters of 8, 12, and 16 mm. Detailed TEM confirmed that there was a negligible difference in the thickness of the intermetallic layer formed at the dissimilar joint interface for AW and PWHT joints. While the intermetallic phases formed at the joint interface comprised Al₃Ti, τ (Ti₂Mg₃Al₁₈), and Al in AW joints, they consisted of Al+τ or Mg₂Al₃+τ+Al in PWHT joints. Softened regions were generated in 7075 base material immediately next to the interface in AW joints. Post­weld heat treatment increased the hardness of the softened region almost to that of as received 7075–T6 base material in 12 and 16 mm diameter joints. In contrast, the hardness of the softened region in 8 mm diameter joints could not be recovered to that of the as received material. This was a result of overaging and coarse precipitates in the softened region produced during the friction welding operation.     

Investigation of the strength of steel–titanium diffusion welded joints

The results of investigation of the structure and mechanical properties in tensile loading and structural strength at 20°C of diffusion welded joints between 08Cr18Ni10Ti steel and PT-3V and PT-5V are presented.     

On the mechanism of twin formation in Fe–Mn–C TWIP steels

Although it is well known that Fe–Mn–C TWIP steels exhibit high work-hardening rates, the elementary twinning mechanisms controlling the plastic deformation of these steels have still not been characterized. The aim of the present study is to analyse the extended defects related to the twinning occurrence using transmission electron microscopy. Based on these observations, the very early stage of twin nucleation can be attributed to the pole mechanism with deviation proposed by Cohen and Weertman or to the model of Miura, Takamura and Narita, while the twin growth is controlled by the pole mechanism proposed by Venables. High densities of sessile Frank dislocations are observed within the twins at the early stage of deformation, which can affect the growth and the stability of the twins, but also the strength of these twins and their interactions with the gliding dislocations present in the matrix. This experimental evidence is discussed and compared to recent results in order to relate the defects analysis to the macroscopic behaviour of this category of material.     

Effect of barium on the phosphorus content of deposited metal of welded joints in cold‐resistant steels

The methods of producing two-layer pipelines of different design, including bimetallic pipes, consisting of carbon and high-alloyed stainless steels, are investigated. It is shown that at optimum design, the welded joints in the pipes should be distributed in a zigzag order so that the welded joints on the external and internal pipes are away from each other.     

Increasing the load‐carrying capacity of spot welded joints in low‐carbon steels

It is shown to be possible to produce a heat-resisting coating for an intermetallic titanium alloy with the hardening ortho phase preventing changes in the surface layer of the alloy as a result of the build-up of oxide corrosion products, which can soften the component at working temperatures of 700–800°C. The results of investigation of the heat resistance properties, evolution of the composition and structure of the alloyed ion-plasma coatings on the titanium alloy with the hardening ortho-phase at working temperatures show that the deposition of the coating greatly reduces the depth in which the surface layer of the alloy changes and the thickness of this layer does not exceed 5 μm.     

Microstructures of 2219 twin wire welded joints

0IntroductionAs a kind of efficient welding method,twin wirewelding has many merits such as big deposition rate,littleheat input and narrow heat-affected zone.What’s more,the defects such as incomplete penetration,discontinuousseam or undercut can be avo…