Effect of the design of the lap welded joint on its stress–strain state

The results of calculation of the stress–strain state of lap welded joints confirm that the design of the joint in bending of the welded layers has a strong effect on the value of the maximum working stresses in longitudinal fillet welded joints.     

Joining phenomena and joint strength of friction welded joint between aluminium–magnesium alloy (AA5052) and low carbon steel

Abstract

The joining phenomena and the joint strength of an Al–Mg alloy (AA5052) and low carbon steel (LCS) friction welded joints were investigated. The weld interface of the LCS side at a friction time of 1·2 s had a slightly transferred AA5052, and then the entire weld interface had it at a friction time of 3·0 s or longer. The joint efficiency increased with increasing friction time, but it decreased at a friction time of 12·0 s or longer. The joint at a friction time of 3·0 s with forge pressure of 190 MPa had 100% joint efficiency and the AA5052 base metal fracture with no crack at the weld interface. The weld interface of these joints also had no intermetallic compound. On the other hand, the joint at a friction time of 8·0 s, which had ～97% joint efficiency, fractured between the AA5052 side and the weld interface because it had the intermetallic compound at the weld interface.     

Influence of alloy elements on microstructure and mechanical property of aluminum–steel lap joint made by gas metal arc welding

5052 aluminum alloy sheets and galvanized mild steel sheets were joined in lap configuration by alternate-current double pulse gas metal arc welding with pure Al, Al–5Si, Al–12Si and Al–4.5Mg (wt%) filler wires. The effect of alloying elements on the microstructure of intermetallic compounds (IMC) layers formed between weld seam and steel, and tensile strength of the resultant joints were investigated. The thickness of IMC layer in all samples varied along the cross-section of the joint, the intermediate part of the IMC layer was thicker than the head and root parts. The diffusion of Si into Fe₂Al₅ sub-layer could restrain the growth of Fe₂Al₅ sub-layer and IMC layer, and joint's mechanical property improved with the increasing Si content in Fe₂Al₅ phase. Due to the high hot crack sensitivity of Al–4.5Mg alloy, cracks generated at the root of joint made with Al–4.5Mg filler, resulting in poor mechanical property.     

Effect of roll-bonding temperature on the strength and electrical conductivity of an α-brass-clad Cu–1Cr alloy composite

Tri-layered α-brass-clad Cu–Cr-alloy composite plates were prepared by hot roll-bonding. Neither intermetallic-compound layers nor interface defects were observed at the interfaces in the as-rolled and heat-treated α-brass-clad Cu–Cr composite plates. The hardness of the as-rolled α-brass layer was greater than that of the Cu–Cr substrate, since the α-brass was strengthened by strain hardening more efficiently upon rolling. The hardness of the α-brass decreased appreciably upon annealing because of the recovery processes, whereas that of the Cu–Cr layer slightly increased after heat treatment at 450°C due to the precipitation strengthening. After the post-roll-bonding heat treatment at 450°C, the strength of the α-brass-clad Cu–Cr-alloy composite decreased with a significant increase in ductility. The electrical conductivity of the asroll-bonded α-brass clad Cu–Cr alloy composite (47–52% IACS) increased significantly (to 72–74% IACS) after the 1-h heat treatment. The strength and conductivity of the clad composite are dependent on the precipitation strengthening of Cu–Cr and recovery softening of α-brass in the course of the post-roll-bonding heat treatment.     

Influence of holding time on microstructure and shear strength of Mg alloy/steel joint diffusion bonded with Zn－5Al interlayer

The diffusion bonding of AZ31B Mg alloy and Q235 steel was investigated with a Zn-5Al alloy as interlayer and under different holding time ranging from 3 to 1 200 s.The microstructure and phase compositions of bonded joints were characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) methods.The shear strength of Mg alloy/steel joints was measured by tensile tester.It was found that the microstructure of bonded joints evolved dramatically along with the prolongation of holding time.Under the holding time of 3 s, the main part of joint was composed of MgZn2 phase and dispersed Al-rich solid solution particles.When increased the holding time more than 60 s, the excessive solution of AZ31B into the interfacial reaction area led to the formation of coarse phase and eutectic microstructure, and also the complex Fe-Al and Mg-Al-Zn IMCs at transition layer closed to Q235 steel side.According to the tensile testing characterizations, the joints obtained under holding time of 3 s exhibited the best shear strength of 84 MPa, and the fracture occurred at the intermediary part of joint where the flexible Al-rich solid solution particles could help to impede the microcrack propagations.With prolonging the holding time to 600 s, the shear strength of joints was deteriorated enormously and the fracture position was shifted to the transition layer part closed to Q235 steel.     

Effect of technological parameters on the mutual penetration of copper and iron in laser cladding of steel with a copper–nickel alloy

A copper–nickel alloy was deposited on steel using a powerful fibre laser. Beads of different height and width were produced by varying the process parameters. The results of metallographic examination show that at optimum cladding conditions there are areas of unmelted steel. In areas where the steel is melted the penetration depth, the width of the transition zone from steel to copper, the depth of penetration of the cracks caused by the Rehbinder effect and the content of the iron phase in the copper layer are lower than in other conditions.     

Microstructure and bonding strength of Ni-based alloy coating

Glass molding dies often fail due to wear, oxidation and crack under the service condition of the melting glass above 1100℃ , existence of thermal shock or sliding contact friction. A repeated phase transformation may occur because the surface temperature of the die cavity exceeds eutectoid temperature during the service once the die is in contact with the hot glass. This, in turn, results in cracking on the die cavity surface, and finally, the service life of the die will be reduced[1]. Aust…     

Effect of tension deformation on microstructure and mechanism of electrodeposited nickel coating

Nickel coating deposits with better ductility on a lower carbon steel sheet were produced by electrodeposition method and the electrodeposited nickel coating was deformed with the strain of 10%. Then the surface morphology, the deformation texture and the mechanical properties were analyzed by scanning electron microscopy （SEM）, X-ray diffractometry （XRD） and nano-indentation measurement, respectively. The principle of nano-indentation to measure the hardness and elastic modulus of nickel coating was introduced. The relation curves of the load and displacement were obtained, including the original electrodeposited samples and the samples under tension. The results show that： 1） there are only two main texture components Ni （111） and Ni （200） in the nickel coating, and no new texture component is found due to the elongation; 2） after tensile deformation in the coating, the surface roughness increases and the microcrack is found; 3） The hardness and the elastic modulus decrease after tensile deformation; and 4） for the original electrodeposited sample, the indentation depths change with the load, the hardness and the elastic modulus decrease with the increase of the depth. In addition, the investigation of creep shows that the value of creep increases when the tensile strain ε〉 10%.     

Effect of Cu on the evolution of precipitation in an Fe–Cr–Ni–Al–Ti maraging steel

The evolution of precipitates in an Fe–Cr–Ni–Al–Ti stainless maraging steel alloyed with Cu was investigated during aging at 525 °C. Atom probe tomography was used to reveal the development of precipitates and to determine their chemical composition. Two types of precipitates were observed to form during the aging process. Based on their chemical composition these are assumed to be NiAl B2 and Ni₃(Ti,Al) (η-phase). The two phases of precipitates were found to develop independently of each other and the addition of Cu was found to accelerate precipitation. However, the effect of Cu on the nucleation of these phases is different: on the one hand, in the case of NiAl, Cu is incorporated and thus reduces the activation energy by reducing the lattice misfit; on the other hand, Cu acts as a nucleation site for the precipitation of Ni₃(Ti,Al) by forming independent Cu clusters.     

Effect of trace Ag on the microstructure and precipitation of an Al–Cu–Mg alloy

Abstract

This paper investigated the effect of different amounts of Ag addition on the microstructure, properties and precipitation processes of Al–4·6Cu–6·9Mg(wt-%) alloy using various analytical methods. It was found that Ag addition stimulated new X′ 9 and Ω phases precipitated finely and dispersively in the matrix, as a result of Mg–Ag co-clusters; the volume fraction of precipitates increased with the content of Ag addition. Such precipitation improved the mechanical performance of the Al–Cu–Mg alloy significantly. The mechanism for the formation of new precipitates is also described in this paper.     

Effect of sulphides on corrosion of Cu–Ni–Fe–Mn alloy in sea water

Abstract

The corrosion behaviour of Cu–30Ni–2Fe–2Mn commercial alloy (similar to C71640) in quiescent, hermetically closed sulphide polluted and unpolluted natural sea water at 25°C was investigated. The corrosion resistance was examined using free corrosion and electrochemical tests and the surface film was characterised by chemical analysis and X-ray photoelectron spectroscopy. The different susceptibilities to corrosion were closely linked to the initial sulphide concentration; the accelerated attack occurring with an initial sulphide concentration of 4 ppm correlated with the amount of dissolved oxygen in solution and with the chemical composition of the corrosion layer.     

Effect of modifying additions on the ductility and plastic properties and the brittle strength of cold‐resistant,low‐alloy steel

The special features of contact-reactive soldering of crystals to the bodies of devices are investigated. The methods of soldering crystals to the bodies of power semiconductor devices with the formation of the Si–Au, Al–Zn, and Zn–Sn eutectics are analysed. New methods of lead-free contact-reactive soldering of crystals with the formation of Si–Au, Al–Zn, Zn–Sn, and Al–Zn–Sn eutectics were developed and tested.     

Microstructure and shear strength of the brazed joint of Ti（C,N）-based cermet to steel

Firm joins were obtained between Ti(C,N)-based cermet and steel with Ag-Cu-Zn-Ni filler metal by vacuum brazing. The effects of technological parameters such as brazing temperature, holding time, and filler thickness on the shear strength of the joints were investigated. The microstructure of welded area and the reaction products of the filler metal were examined by scanning electron microscopy (SEM), metallographic microscope (OM), energy-dispersive X-ray analysis (EDS), and X-ray diffraction (XRD). The brazing temperature of 870°C, holding time of 15 min, and filler thickness of 0.4 mm are a set of optimum technological parameters, under which the maximum shear strength of the joints, 176.5 MPa, is achieved. The results of microstructure show that the wettability of the filler metal on Ti(C,N)-based cermet and steel is well. A mutual solution layer and a diffusion layer exist between the welding base materials and the filler metal.     

Improving the shear strength of Sn–Ag–Cu–Ni/Cu–Zn solder joints via modifying the microstructure and phase stability of Cu–Sn intermetallic compounds

This study focuses on the correlation between high-speed impact tests and the interfacial reaction in Sn-3.0Ag-0.5Cu-0.1Ni/Cu (wt%) and Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints. Adding Ni into the Sn–Ag–Cu solder alters the interfacial morphology from scallop type to layer type and exhibits high shear strength after reflow in both solder joints. However, the shear strength of Sn-3.0Ag-0.5Cu-0.1Ni/Cu solder joints degrades significantly after thermal aging at 150 °C for 500 h. It is notable that Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints still present higher shear strength after aging at 150 °C. The weakened shear strength in Sn-3.0Ag-0.5Cu-0.1Ni/Cu solder joints is due to stress accumulation in the interfacial (Cu,Ni)₆Sn₅ compound induced by the phase transformation from a high-temperature hexagonal structure (η-Cu₆Sn₅) to a low-temperature monoclinic structure (η'-Cu₆Sn₅). However, doping small amounts of Zn into (Cu,Ni)₆(Sn,Zn)₅ can inhibit the phase transformation during thermal aging and maintain strong shear strength. These experiments demonstrate that Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints can act as a stable connection in the micro-electronic packaging of most electronic products at their average working temperatures.     

Effect of intermetallic compounds on heat resistance of hot roll bonded titanium alloy–stainless steel transition joint

The effect of intermetallic compounds on the heat resistance of transition joint was investigated. The experiment of post-weld heat treatment for the hot roll bonded titanium alloy–stainless steel joint using nickels interlayer was carried out, and the interface microstructure evolution due to heat treatment was presented. There was not found significant interdiffusion at stainless steel/nickel interface, when the specimens were heat treated in the temperature range of 600–800 °C for 10 and 30 min, while micro-cracks occurred at the stainless steel/nickel interface heat treated at 700 °C for 30 min. The thickness of intermetallic layers at nickel/titanium alloy interface increased at 600 °C, and micro-cracks occurred at 700 and 800 °C. The micro-cracks occurred between intermetallic layers or between intermetallic layer and nickel interlayer as well. The tensile strength of the transition joint decreased with the increase of heat treatment temperature or holding time.     

First-principles investigation of the Cu–Ni,Cu–Pd,and Ni–Pd binary alloy systems

Phase diagrams of copper–nickel–palladium binary alloys were determined by density functional theory cluster expansion method. The system has both magnetic and non-magnetic binaries and subtle phase coexistence areas between similar and different kind of lattice types. Furthermore, the CuPd binary has several ordered structures. Cluster expansion models were constructed by heuristic cluster selection for all of the fcc structures and for the CuPd_bcc structure. Both configurational and magnetic phase diagrams were determined. Small amount of nickel magnetize fcc palladium to 0.26 μ_B from which the magnetic moment rises almost linearly to that of pure Ni. In CuNi, 0.46 x-Ni is needed for the magnetic transition. In CuPd alloy in 0 K, configurational free energy difference between bcc and fcc lattice resulting to phase separation is only about 1.1 kJ/mol-atoms. Low temperature energetics and magnetic phase diagrams have good quantitative agreement with available experimental and theoretical results. Finite temperature properties of the alloys are in good qualitative agreement with experimental results.     

Influence of pickling time on electroless Ni–P coating on magnesium alloy

In this study, a simple pickling process in H₃PO₄ and NH₄HF₂ solution was used for electroless Ni–P plating on AZ61 magnesium alloy. It is found that the corrosion rate of magnesium alloy during pickling significantly decreased because NH₄HF₂ was added into H₃PO₄ pickling solution. Ni–P coating plated only with pickling process shows poor adhesion because of the low F/O ratio of the substrate surface. However, F/O ratio, adhesion, and corrosion resistance of Ni–P coating are obviously enhanced after pickling followed by activation. The optimal pretreatment process is pickling for 120 s and activation for 4 min, under which the Ni–P coating has an optimum F/O ratio of 1.8 and the coating gets a dense structure, better adhesion, and higher corrosion resistance.     

Ni–P coating on AZ31 magnesium alloy and its crystallization

Amorphous Ni-P coating was plated on AZ31 magnesium alloy via the electroless plating technique, and the plated alloy was subsequently annealed. X-ray dif- fraction （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, and differential scanning calorimetry （DSC） were used to characterize the coating. The results show that the hardness of the coating is much higher than that of bare magnesium alloy, which further increases after crystallization. The electrochemical polarization and salt spray tests show that the coating exhibits a much higher corrosion resistance than that of the bare magnesium alloy. Moreover, the crystallized coating still exhibits a much stronger corrosion resistance than that of the bare magnesium alloy, although its corrosion resistance is lower than that of the as-plated one.     

Effect of coating repair on microstructure and mechanical properties of Ni3Al based alloy IC6

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