Wrought Sheet Research Articles

Fatigue crack initiation and propagation in plain and notched PBF-LB/M, WAAM, and wrought 316L stainless steel specimens

Additively manufactured (AM) components—either made by laser-powder bed fusion or wire and arc additive manufacturing—typically contain process-related defects on and near surfaces that can be removed by machining. Various studies have shown that post-treatment, such as machining significantly improves the fatigue strength of AM parts. To this day, however, hardly any studies have investigated the fatigue strength of post-treated additively manufactured components with notches. In this study, fatigue tests were performed on plain and notched specimens to determine and compare the crack initiation and crack propagation behavior due to different manufacturing-related effects. Tests were performed on specimens produced by the two aforementioned AM processes and compared to specimens taken from wrought sheets. The fatigue strength of AM materials is influenced by microstructure, defects, residual stress, and notches. PBF-LB/M specimens exhibit the highest fatigue strength in plain, notch-free conditions, attributed to differences in microstructure and static strength affecting fatigue crack initiation. Notched specimens show larger differences among materials, with PBF-LB/M having shorter fatigue crack propagation life related to line-type defect clusters, while the plain PBF-LB/M specimens are less affected as their fatigue strength is primarily determined by fatigue crack initiation.

Joint integrity evaluation of laser beam welded additive manufactured Ti6Al4V sheets

The feasibility of joining laser metal deposited Ti6Al4V sheets using laser beam welding was investigated in this article. The additive manufactured sheets were joined using a 3 kW CW YLS-2000-TR ytterbium laser system. The mechanical properties and microstructure of the welded additive manufactured parts (AM welds) were compared with those of the wrought sheets welded using the same laser process. The welds were characterized and compared in terms of bead geometry, microhardness, tensile strength, fractography, and microstructure. The differences in characteristics are majorly found in the width of the bead and tensile strength. The bead width of AM welds appear wider than the wrought welds, and the wrought welds exhibited higher tensile strength and ductility than the AM welds.

Research on the influence of deformable sheet aluminum alloy rheological behavior on stretch forming process limits

Our research was aimed at modeling a symmetrical wrapping and stable control of the processes of shaping by wrapping a sheet blank along a wrapping punch having a double curvature surface and placed on the table of a virtual stretch-tightening press. The main task of modeling was to determine the deformed state with a uniform change in thickness in different regions of the sheet blank without folds and breaks, but without the influence of the rheological behavior of the deformable aluminum alloy. Here, the LS-DYNA software package is used with the use of an explicit or implicit solver for nonlinear problems of solid mechanics, characteristic of nonequilibrium transitions of the initial dissipative phase due to viscosity and heat transfer. Now it is possible to predict defect formation from a practical point of view, using the forming limit diagram (FLD), which makes it possible with sufficient accuracy to determine the degree of deformation of a given sheet material, at which any defects do not occur. The presented results of the study revealed the features of the influence of the rheological behavior of a wrought sheet aluminum alloy on the limits of the shaping process by a wrap.

Development of a laboratory-scale Upset Protrusion Joining (UPJ) system for dissimilar materials

Magnesium alloys have a significant benefit over steel and aluminum alloys in manufacturing components for many automotive and structural applications because of their higher light-weighting potential, lowest density, and higher strength to weight ratio. However, one of the impediments to the success of multi-material integration of the above materials for automotive manufacturing is joining these materials together without any cracking or corrosion during in-service use. The present work aims to develop and demonstrate a cost-effective, novel, and versatile mechanical joining technique, named Upset Protrusion Joining (UPJ), to mechanically and rapidly join a cast magnesium component to an aluminum alloy sheet. The process involves a cylindrical protrusion emanating perpendicular to the flat surface of a cast plate that fits through a hole in an aluminum sheet. The two components are then clamped together, electrically heated, and compressed perpendicular to the protrusion axis. During compression, the protrusion expands circumferentially to fill the hole as well as the region above the hole, thus entrapping the sheet metal between the mushroomed head and the casting. The effect of different UPJ process parameters such as applied current, current duration, compression loading rate, and compression distance were studied through experimentation on die-cast magnesium alloy, with protrusion of 11 mm diameter and 14 mm height. Material-specific process window was identified to achieve a satisfactory joint quality in terms of post-UPJ joint strength with appearance. UPJ method shows a great promise to implement in automotive and other industrial manufacturing environments for fastening cast components to a similar or dissimilar wrought sheet component.

High-throughput stochastic tensile performance of additively manufactured stainless steel

An adage within the Additive Manufacturing (AM) community is that “complexity is free”. Complicated geometric features that normally drive manufacturing cost and limit design options are not typically problematic in AM. While geometric complexity is usually viewed from the perspective of part design, this advantage of AM also opens up new options in rapid, efficient material property evaluation and qualification. In the current work, an array of 100 miniature tensile bars are produced and tested for a comparable cost and in comparable time to a few conventional tensile bars. With this technique, it is possible to evaluate the stochastic nature of mechanical behavior. The current study focuses on stochastic yield strength, ultimate strength, and ductility as measured by strain at failure (elongation). However, this method can be used to capture the statistical nature of many mechanical properties including the full stress-strain constitutive response, elastic modulus, work hardening, and fracture toughness. Moreover, the technique could extend to strain-rate and temperature dependent behavior. As a proof of concept, the technique is demonstrated on a precipitation hardened stainless steel alloy, commonly known as 17-4PH, produced by two commercial AM vendors using a laser powder bed fusion process, also commonly known as selective laser melting. Using two different commercial powder bed platforms, the vendors produced material that exhibited slightly lower strength and markedly lower ductility compared to wrought sheet. Moreover, the properties were much less repeatable in the AM materials as analyzed in the context of a Weibull distribution, and the properties did not consistently meet minimum allowable requirements for the alloy as established by AMS. The diminished, stochastic properties were examined in the context of major contributing factors such as surface roughness and internal lack-of-fusion porosity. This high-throughput capability is expected to be useful for follow-on extensive parametric studies of factors that affect the statistical reliability of AM components.

Transformation of cast A356 ingots to wrought sheets with enhanced mechanical and tribological properties by different thermo-mechanical processing routes

The dendritic microstructure with non-uniform distribution of hard second phase particles degrades the mechanical and tribological properties of AlSi alloys. Severe plastic deformation methods are found effective in refining microstructure and enhancing the material properties. In our present study, two different thermo-mechanical processing routes were employed on a cast hypo-eutectic AlSi alloy to produce wrought sheets with refined microstructure. In one processing route, the material is subjected to cryorolling after solution treatment and in the other route, the material is subjected to a thermal-treatment between solution treatment and cryorolling. Cryorolling imposes severe plastic deformation onto the material resulting in refinement and redistribution of second phase particles leading to enhanced strength and ductility. Cryorolling with pre-roll thermal-treatment resulted in finer grain structures than the material without thermal-treatment. The tribological behaviour of processed materials are studied and compared with the base materials by pin-on-disk method. Maximum wear resistance is observed in thermal-treated material followed by cryorolled material with pre-roll thermal-treatment. Transformation from adhesion wear to oxidative-delamination wear is found to be the primary reason for the enhanced wear resistance in thermal-treated material. The various wear mechanisms involved are explained in detail based on the microstructural evolution and mechanical properties.

Effect of adhesive on fatigue property of Aural2 to AA5754 dissimilar aluminum alloy resistance spot welds

Abstract General Motors (GM) has developed a proprietary resistance spot welding (RSW) process using a multi-ring, domed electrode geometry that has been used successfully in automotive aluminum welding operations. To enhance structural performance, one-part epoxy adhesives are frequently applied prior to RSW to create weld-bonded joints. The addition of adhesive can result in additional porosity created within the weld nugget. Therefore, the adhesive's impact on mechanical properties, especially fatigue properties requires further investigation. Load-controlled fatigue testing was conducted on dissimilar aluminum alloy spot welds made of AA5754 wrought sheet and Aural2 die casting sheet with and without the addition of adhesive prior to welding. The same GM RSW electrode and weld schedule was used for both conditions. The results show that the addition of adhesive results in a larger nugget size, but similar maximum load in tension-shear testing. X-ray computed tomography during interrupted fatigue testing of the spot welds shows that the main fatigue crack initiates at the edge of the nugget in the plane of the faying interface and penetrates through the Aural2 die cast sheet in the thickness direction. Using the structural stress concept, it was also found that the structural stress range–fatigue life curve for these spot welds, both with and without adhesive, falls onto a single master curve indicating that the nugget size which corresponds to the tensile and bending strength dominates the fatigue life and that adhesive-induced porosity within the weld nugget does not harm fatigue performance.

Mechanical Properties and Fracture Behaviour of LMD Produced 2.4682 and Wrought 2.4630 Dissimilar Welds

A bearing made of Stellite 31 (2.4682) has to be welded onto a housing of Nimonic 75 (2.4630) by autogenous laser beam welding. The bearing part is produced by laser metal deposition (LMD), the housing consists of wrought sheet metal. An investigation is undertaken in order to study the effect of the anisotropy of the LMD part on the weld quality. Tensile specimens were produced and tested under varying load directions and test temperatures, and application of different weld heat treatments. The fractured specimens were analysed by metallography and fractography. Tensile tests at room temperature show a dependency of the fracture location and the mode of failure on the load direction with respect to the layer direction in conjunction with the heat treatment. At elevated temperature of 750° all specimens broke in the base material of 2.4630 in ductile fracture mode. Strength measured supersedes the values of either of the base materials.

Fatigue Behavior of Dissimilar Aluminum Alloy Spot Welds

With the broader utilization of a variety of aluminum alloys in the automotive industry for structural lightweight applications, the need for resistance spot welding (RSW) of dissimilar aluminum alloys is increasing. General Motors (GM) has developed a proprietary RSW process using a multi-ring, domed electrode geometry that significantly improves the performance of the aluminum resistance spot welds. In addition, to enhance structural performance, epoxy adhesivesare also often applied prior to RSW to obtain weld-bonded joints.As a contribution, the load-controlled fatigue behavior of dissimilar aluminum alloy spot welds made of 2mm thick AA5754 wrought sheet and 3mm thick Aural2 die casting sheet with and without the addition of adhesive prior to welding was studied. The same GM proprietary resistance spot welding electrode and current schedule was applied to both welding conditions leading to a larger nugget size when using adhesive, but both weld configurations presented similar maximum load in tension-shear testing. X-ray computed tomography was used to detect internal welding discontinuities such as voids and also to follow the damage evolution and fatigue crack initiation and growth during interrupted fatigue testing of the spot welds. The results show that the main fatigue crack initiates at the edge of the nugget and penetrates through the Aural2 die casting sheet in the thickness direction. Using the structural stress concept, it was also found that the structural stress-fatigue life curve for AA5754 to Aural2 aluminum spot welds with and without adhesive falls into a master curve indicating that the nugget size which corresponds to the tensile and bending strength dominates fatigue life.

Local plastic strain inhomogeneity in a ZEK100 Mg alloy

Magnesium alloys have great potential for lightweighting applications in the transportation industry. It is known, however, that Mg and Mg-alloys exhibit large plastic strain heterogeneity. Such heterogeneity is important both from the perspective of formability and fracture if such sheet materials are to be stamped. Also, such observations are important for our fundamental understanding of how plasticity spreads in such materials. In this work we have sought to couple together local plastic strain measurements using digital image correlation with full-field crystal plasticity simulations with the idea of identifying and quantifying the plastic strain heterogeneity. A recently developed ZEK-100 alloy has been studied, as this alloy has shown promise as a wrought sheet product.

Strain rate sensitivity and fracture behavior of severely deformed Al–Mn alloy sheets

► Aluminum alloy 3003 was processed by constrained groove pressing (CGP) technique. ► Strain rate sensitivity values increase with increasing imposed strain by CGP. ► Fracture behavior changes with imposed strain. ► Shear fracture angle increases with increasing of CGP pass number. Wrought sheets of an Al–Mn alloy are subjected to severe plastic deformation using constrained groove pressing (CGP) method. After applying CGP passes on the sheets, tensile tests at different strain rates are carried out and the strain rate sensitivity values are calculated. Results show that strain rate sensitivity is increased from 0.0081 in annealed sheets to 0.019 after three passes of constrained groove pressing. This arises from intrinsic decrease in grain size due to severe straining. Experimental results reveal that after three CGP passes, the rate of increasing in strain rate sensitivity is decreased. Fracture surfaces of the tensile samples are observed using scanning electron microscopy. It is found that with increasing pass number, shear fracture angle is increased from 45° for annealed sample to 60° after three passes of CGP. This is due to the change in the mechanism of fracture from tensile fracture to shear fracture which is detectable from the formation of parabolic dimple instead of hemispherical equiaxed ones.

Effect of microalloying (Ca, Sr, and Ce) on elevated temperature tensile behavior of AZ31 magnesium sheet alloy

The effect of microalloying with calcium, strontium, and cerium on the microstructure and the elevated temperature deformation behavior of magnesium sheet alloy AZ31 was investigated. Base composition and microalloyed AZ31 materials were cast and rolled into wrought sheet by an identical thermo-mechanical process. A series of hot tensile tests (temperatures of 300 °C, 400 °C, and 450 °C; constant true strain rates of 0.1 s −1, 0.01 s −1, 0.001 s −1, and 0.0003 s −1) were performed to characterize the deformation behavior of the sheet alloys. Interrupted tensile tests were used to study microstructural evolution with strain. A well-dispersed and thermally stable second phase produced by microalloying refines, stabilizes the grain structure, and significantly enhances hot formability of AZ31 sheet. The enhancement is most pronounced under deformation conditions of 450 °C and; 0.0003 s −1 strain rate, with tensile elongation increasing from 347% for the base alloy, to 406% with Ca only, 437% with Ca and Ce, and 552% with Ca, Sr and Ce for microalloyed AZ31 alloys. The second phase particles resist grain coarsening, promote grain boundary sliding, retard strain localization or necking, and postpone cavitation to higher strain levels to achieve this improvement in formability.

The effects of microstructural features on the performance gap in corrosion resistance between bulk and HVOF sprayed Inconel 625

It is commonly observed that there is a performance gap between the corrosion resistance of thermally sprayed coatings and the equivalent bulk material. This is attributed to the significantly modified microstructure of the sprayed coatings. However, currently there is no detailed understanding of which aspects of microstructural modification are primarily responsible for this performance gap. In this work several deliberately microstructurally modified versions of the Ni-based superalloy Inconel 625 were produced. These were subjected to potentiodynamic electrochemical testing in 0.5 M H 2SO 4 to investigate the links between specific microstructural features and electrochemical behaviour. Samples were prepared by high-velocity oxy-fuel (HVOF) thermal spraying, laser surface remelting using a high power diode laser and conventional powder sintering. Microstructural features were examined by optical and scanning electron microscopy and X-ray diffraction. Potentiodynamic testing was carried out on the following forms of Inconel 625: wrought sheet; HVOF sprayed coatings; sintered powder compacts; laser melted wrought sheet and HVOF sprayed coatings. Using the corrosion behaviour, i.e. passive current density, of the wrought sheet as a baseline, the performance of different forms of Inconel 625 was compared. It is found that a fine dendritic structure (with associated microsegregation) produced by laser remelting wrought sheet has no significant effect on corrosion performance. Up to 12% porosity in sintered powder samples increases the passive current density by a factor of only around 2. As observed previously, the passive current density of HVOF sprayed coatings is 20–40 times greater. However, HVOF coatings subjected to laser surface remelting are found to have a passive current density close to that of wrought material. It is concluded that, whilst porosity in coatings produces some decrease in corrosion resistance, the main contributing factor is the galvanic corrosion of localised Cr-depleted regions which are associated with oxide inclusions within HVOF sprayed samples.

Implementing the Direct Powder Route for Titanium Mill Product: Continuous Production of CP Sheet

Major research and development efforts both in CSIRO and elsewhere aim to develop processes for commercial production of low cost titanium powder. These processes could reduce the current cost of titanium, but the major savings are expected to come by enabling powder metallurgical processes which transform these powders into products. Powder metallurgical (PM) processes (e.g. CIP/HIP) are well established for discrete components, but technologies for continuous production of “mill” product are immature. New processes will be needed for the economic manufacture of mill product (e.g. sheet and tube) from the large quantities of low-cost powder which will become available when the emerging powder production processes enter commercial production. The paper will present a process for the production of commercial purity (CP) sheet by direct rolling of powder. It is novel in that it avoids both the use of binders and densification via batch sintering. A roll compacted green sheet is rapidly heated under a controlled atmosphere before being consolidated to nominally 100% density by hot rolling. Following conventional batch annealing, strip samples exhibit properties approaching those of commercial wrought sheet of an equivalent grade. In order to achieve this, a number of key variables including powder chemistry, morphology and particle packing, the roll compaction and hot rolling parameters needed to be understood and closely controlled.

Effects of heat input on microstructure and tensile properties of laser welded magnesium alloy AZ31

A 3 kW CO 2 laser beam was used to join wrought magnesium alloy AZ31 sheets, and the effects of heat input on the quality of butt welding joints were studied. By macro and microanalysis, it is found that the welding heat input plays an important role in laser welding process for AZ31 wrought sheets. After welding, the grains far from the weld centre present the typical rolled structure. But the microstructure out of the fusion zone gradually changes to complete equiaxed crystals as the distance from the weld centre decreases. Adjacent to the fusion boundary, there is a band region with columnar grains, and its growth direction is obviously perpendicular to the solid/liquid line. The microstructure in fusion centre consists of fine equiaxed grains and the many precipitated particles are brittle phase Mg 17Al 12 or Mg 17(Al,Zn) 12. With increasing the heat input, the band width of columnar grains varies, the grains in fusion zone get coarser, and the distribution of precipitates changes from intragranularly scattered particles to intergranularly packed ones. The results of tensile test show that the change trend of ultimate tensile strength (UTS) and elongation of the welded joints is to increase at first and then decrease with the heat input increasing. When the heat input reaches 24 J mm − 1 , the maximum value of the UTS is up to 96.8% of the base metal.

Macroscopic damage by the formation of shear bands during the rolling and deep drawing of magnesium sheets

Most magnesium parts for automobiles are currently produced by die casting, which allows for complex geometries. However, die casting has two significant disadvantages over wrought alloy sheets: it results in poorer mechanical properties and much rougher surfaces. An alternative production route for these parts is deep-drawn and joined magnesium sheets. This article describes an investigation into the effects of the deep-drawing process on magnesium alloys.

77 to 1200 K tensile properties of several wrought superalloys after long-term 1093 K heat treatment in air and vacuum

The 77 to 1200 K tensile properties of approximately 1.3 mm thick wrought sheet Co-base Haynes alloy 188 and Ni-base Haynes alloy 230 and Inconel 617 have been measured after heat treatment in air and vacuum for periods up to 22,500 h at 1093 K. Significant changes in structure were produced by prior exposures, including precipitation of second phases and, in the case of heat treatment in air, oxide scale and surface-connected grain boundary pits/oxides, as deep as 50 to 70 µm, in all three superalloys. Due to the geometry of the experiment, the vacuum-exposed samples were protected from loss of volatile elements by evaporation; hence, such specimens were simply given 1093 K anneals in an innocuous environment, which produced very little surface attack. Compared to the properties of as-received alloys, prior exposure tended to reduce both the yield strength and ultimate tensile strength, with the greatest reductions at 77 and 298 K. The most dramatic effect of heat treatment was found in the low-temperature residual tensile elongation, where decreases from 40 to 5% at 77 K were found. Ductility is the only property that was found to have a consistent dependency on environment, with air exposure always yielding less tensile elongation than vacuum exposure.

Strain softening behaviour of Pb–0.064Ca–0.44Sn wrought sheet

Abstract Strain softening in a wrought Pb–Ca–Sn battery alloy is explained by the formation of shear bands during subsequent deformation. It is shown that these bands develop as a result of geometric softening, but once they exist the localized deformation in these bands causes shearing and subsequent dissolution of precipitates producing a substantial loss of strength. Adiabatic heating in the shear bands promotes localized dissolution of precipitates and recrystallization. As the reduction in rolling is increased the number of shear bands increases while their strength decreases. This leads to a decrease in maximum tensile strength and an increase in elongation to fracture.

Structure and property relationships of Ni−20Cr produced by high−rate physical vapor deposition

In high−rate physical vapor deposition (HRPVD) processes, a change in substrate temperature produces a marked change in microstructure, mechanical properties, and hardness of the deposits. By varying this parameter, the relationship between microstructure and mechanical properties of vapor−deposited Ni−20Cr sheets was investigated. These sheets were characterized by grain size, grain morphology, density, tensile properties, bend ductility, and hardness. The grain morphology of deposited sheets at different substrate temperatures was in agreement with the morphology zone model suggested by Movchan and Demchishin. Samples of wrought (cast, rolled, and annealed) sheets from the same material were characterized by the same procedures to form a basis of comparison for deposited sheets. The investigation of mechanical properties and Hall−Petch relationship showed that deposited material was very similar to rolled and annealed material and constitutes a true engineering material.

Effect of Alloying Additions on Sea Water Corrosion Resistance of Iron-Aluminum Base Alloys

Abstract Wrought sheet corrosion specimens of varying aluminum (6 to 16%), molybdenum (to 8%), chromium (to 2%), copper (to 3%) and nickel (to 3%) were exposed to ambient and boiling sea water. Cor...