UNS A92024 Research Articles

Preliminary Evaluation of a Multipass Strategy in Abrasive Waterjet Machining of an Alloy UNS A92024

Abrasive waterjet cutting is a valuable method for removing material without causing thermal damage, making it suitable for machining materials of different thicknesses and minimising waste. However, machining thicker materials requires higher flow rates and pressure, resulting in increased energy consumption and surface defects that increase costs. This study proposes a multi-pass strategy to improve the performance of abrasive waterjet machining. The study aims to investigate the impact of the number of passes on the efficiency of machining a thick UNS A92024 alloy. Surface integrity will be evaluated from two perspectives: macrogeometry (such as machining depth and taper) using image processing, and microgeometry (surface roughness). The study will also analyse the relationship between the number of passes and traverse speed to identify the optimal combination and develop a predictive model to enhance overall process performance.

Study of Abrasive Water Jet Machining as a Texturing Operation for Thin Aluminium Alloy UNS A92024.

Surface modification of metallic alloys can create hydrophilic or hydrophobic surfaces that enhance the functional performance of the material. For example, hydrophilic surfaces have improved wettability, which improves mechanical anchorage in adhesive bonding operations. This wettability is directly related to the type of texture created on the surface and the roughness obtained after the surface modification process. This paper presents the use of abrasive water jetting as an optimal technology for the surface modification of metal alloys. A correct combination of high traverse speeds at low hydraulic pressures minimises the power of the water jet and allows for the removal of small layers of material. The erosive nature of the material removal mechanism creates a high surface roughness, which increases its surface activation. In this way, the influence of texturing with and without abrasive has been evaluated, reaching combinations where the absence of abrasive particles can produce surfaces of interest. In the results obtained, the influence of the most relevant texturing parameters between hydraulic pressure, traverse speed, abrasive flow and spacing has been determined. This has allowed a relationship to be established between these variables and surface quality in terms of Sa, Sz and Sk, as well as wettability.

Preliminary study of abrasive water jet texturing on low thickness UNS A92024 alloy sheets

Texturing and surface modification operations are a line of research of great interest nowadays. The requirement to establish a process that can generate a constant and homogeneous roughness as a previous step to joining operations, application of paint or mechanical tests is a current challenge. Technologies such as shot blasting or laser texturing have achieved great results in terms of roughness and surface activation. Nevertheless, there is an alternative technology that is achieving great interest. Abrasive water jet texturing takes advantage of the combination of the impact of abrasive particles and water at high speed with the controlled displacement of the jet to generate a surface with a controlled roughness. Thus, in comparison with other technologies, abrasive waterjet texturing can achieve higher roughness values and a constant texturing area as a function of the overlap established between the passes. In this work, a preliminary study is proposed in order to establish a direct relationship between the parameters governing the technology and the roughness generated in a low thickness UNS A92024 alloy. Defectology associated to the process, as well as the combination of texturing parameters have been determined.

Influence of Tool Wear on Form Deviations in Dry Machining of UNS A97075 Alloy

Geometrical tolerances play a very important role in the functionality and assembly of parts made of light alloys for aeronautical applications. These parts are frequently machined in dry conditions. Under these conditions, the tool wear becomes one of the most important variables that influence geometrical tolerances. In this work, the influence of tool wear on roundness, straightness and cylindricity of dry-turned UNS A97075 alloy has been analyzed. The tool wear and form deviations evolution as a function of the cutting parameters and the cutting time has been assessed. In addition, the predominant tool wear mechanisms have been checked. The experimental results revealed that the indirect adhesion wear (BUL and BUE) was the main tool-wear mechanism, with the feed being the most influential cutting parameter. The combination of high feed and low cutting speed values resulted in the highest tool wear. The analyzed form deviations showed a general trend to increase with both cutting parameters. The tool wear and the form deviations tend to increase with the cutting time only within the intermediate range of feed tested. As the main novelty, a relationship between the cutting parameters, the cutting time (and, indirectly, the tool wear) and the analyzed form deviations has been found.

Preparation and Characterization of a Silane Sealed PEO Coating on Aluminum Alloy

A dense alumina ceramic coating was formed on UNS A97075 Al alloy by plasma electrolytic oxidation (PEO). An efficient and environmentally friendly silane layer was prepared to seal the PEO coating. The scanning electron microscopy (SEM) results showed that the PEO coating was completely sealed by the silane layer. The electrochemical corrosion evolution of the silane sealed PEO composite coating was studied by electrochemical impedance spectroscopy (EIS). Based on the EIS data, the corrosion evolution of the silane sealed composite coating could be divided to three stages during 576 h of immersion test, and the silane coating acted as a good physical barrier in the immersion test, effectively delayed the corrosion process and improved the corrosion resistance.

Analysis of Galvanic Corrosion Current between an Aluminum Alloy and Stainless-Steel Exposed to an Equilibrated Droplet Electrolyte

Measurements of galvanic corrosion between UNS S13800 and UNS A97075 in bulk and equilibrated droplet electrolytes are compared with theoretical predictions of the corrosion current using calculations of the static diffusion-limited current, the classic Cottrell equation, and chemical reaction pathway models. The droplet electrolyte experiments use disks of stainless steel embedded in the aluminum alloy but isolated from electrical contact by an epoxy ring and connected via a zero-resistance ammeter potentiostat. Discrepancies between the measured and expected corrosion current for the droplet electrolyte are analyzed and a mechanism that relies on chemical reactions in the electrolyte to form corrosion products that block ion transport and suppress further oxidation is proposed. Electrochemical impedance spectroscopy and mass measurements are used to monitor changing solution properties in the equilibration of the droplet with the temperature and relative humidity environment of the atmospheric corrosion chamber.

Shrinkage Factor Analysis in the Dry Machining of UNS A92024 Alloy by FEM

Chip evacuation becomes a relevant factor in the dry machining of aeronautical aluminium alloys, either when they are machined as isotropic material or hybridized with other materials. Chip morphology and geometry highly depend on cutting parameters. Several works can be found in the literature focusing on the analysis of chip morphology of aluminium alloys at high cutting speeds but there is a lack of studies that apply low cutting speeds. FEM simulation may be useful to reduce the experimental time and cost of this kind of analysis. Therefore, in this work, the influence of feed-rate on several chip geometrical parameters (height of peaks, height of valleys and shrinkage factor) of dry turned UNS A92024 alloy has been analysed by FEM simulation. Three different energy fracture modes have been tested as damage evolution criterion, in order to get the mode that better fit the experimental chip morphology. In general, the mixed mode was the fracture energy mode that best suited the chip morphology behaviour, within wider feed-rate range.

Cutting parameters influence analysis on fatigue behaviour of dry turned UNS A97075 alloy after corrosion

Aluminum alloys, particularly series 2000 (Al-Cu) and 7000 (Al-Zn), are widely used for structural elements in aircraft. Machining processes are frequently applied in manufacturing these parts. The actual trend in the machining of these components is to reduce or eliminate the use of lubricants, due to environmental reasons. Among the different techniques, dry machining is commonly used for aluminum alloys. However, dry machining generates higher severe cutting conditions, which may negatively affect the surface integrity and the mechanical properties of the machined parts. In this regard, fatigue life is one of the most important mechanical properties to take into account. Micro-cracks generation and nucleation strongly depend on the surface conditions of the machined parts. Additionally, the addition of Zn to pure aluminum (7000 series) reduces the corrosion resistance. Despite its importance, there is a lack of research devoted to analyze the cutting parameters influence on fatigue behaviour, before and after corrosion, in dry machining of these alloys. Therefore, in this work, the cutting speed and feed rate influence on fatigue behaviour of the UNS A97075 (Al-Zn) alloy has been analyzed. Several rotating bar bending fatigue tests have been carried out, studying and comparing the fatigue life curves obtained as a function of the cutting parameters, before and after an immersion corrosion process. The experimental results have revealed that an increment in the cutting speed and feed rate gives rise to fatigue life reduction.

Parametric Analysis of Macro-Geometrical Deviations in Dry Turning of UNS A97075 (Al-Zn) Alloy

Macro-geometrical deviations play a very important role in the functionality and reliability of structural parts for aircraft. The use of environmentally friendly techniques, such as dry machining, may negatively affect these deviations. Despite its importance, there is a lack of research that analyzes them as a function of the cutting parameters in the case of aluminum alloys for aeronautical purpose. In this work, the cutting speed and feed influence on several macro-geometrical deviations (parallelism, straightness, circular run-out, roundness, concentricity, total circular run-out and cylindricity) in dry turning of UNS A97075 alloy was analyzed. The main novelty of this work lies in the use of high slenderness parts used in further fatigue tests. The results showed that feed seems to be the most influential parameter in most of the deviations studied. In addition, the parts with lower rigidity exhibited higher sensitivity to change with the cutting parameters. Finally, different parametric models were proposed to obtain the geometrical deviations as a function of the cutting parameters.

Study of the Tool Wear Process in the Dry Turning of Al–Cu Alloy

Light alloy machining is a widely implemented process that is usually used in the presence of cutting fluids to reduce wear and increase tool life. The use of coolants during machining presents negative environmental impacts, which has increased interest in reducing and even eliminating their use. In order to obtain ecofriendly machining processes, it will be necessary to suppress the use of cutting fluids, in a trend called “dry machining”. This fact forces machines to work under aggressive cutting conditions, producing adhesion wear that affects the integrity of the parts’ surfaces. This study describes cutting tool wear mechanisms in machining of UNS A92024 samples under dry cutting conditions. Energy dispersive spectroscopy (EDS) analysis shows the different compositions of the adhered layers. Roughness is also positively affected by the change of the cutting geometry produced in the tool.

Effect of confined electrolyte volumes on galvanic corrosion kinetics in statically loaded materials

Abstract This work investigates the effects that the confined volume of atmospheric electrolytes has on the galvanic corrosion kinetics of a martensitic stainless steel alloy, UNS S13800, coupled with UNS A97075 in simulated atmospheric environments at relative humidity values that span the range of operational exposures. Restricted volumes found in thin films and droplets have been shown to control reduction reaction kinetics and are an ongoing challenge to characterize and standardize. This, along with the dynamic and high concentration of aggressive ions found in confined electrolytes, creates a unique corrosion system that requires a multifaceted approach to evaluate varied conditions, compare them with traditional measurements, and more accurately predict galvanic atmospheric corrosion. In this work, corrosion currents in galvanic couples were obtained under two environmental conditions: (1) bulk electrolytes, in a standardized test configuration, with chemistries relevant to atmospheric electrolytes; and (2) deliquesced droplets formed and equilibrated at a given temperature and relative humidity value. The corrosion currents for the same galvanic couple specimens were evaluated, using an atmospheric corrosion model, under a thin film electrolyte while statically loaded and unloaded, at two nominally different locations, e.g. Alexandria, VA, and Miami, FL, on the same date, using recorded weather conditions. The modeled corrosion currents were then compared with the currents obtained from the experimental conditions.

One-Shot Drilling Analysis of Stack CFRP/UNS A92024 Bonding by Adhesive.

The use of adhesive layers can improve the properties and reduce the defects produced in the interfaces. This provides adherence to the structure, adapting the joining surfaces and avoiding spaces between the layers. However, the presence of the adhesive can potentiate the defects caused during drilling. In turn, a loss of adhesive in the interface can occur during machining affecting the final structure. This work has followed a conventional OSD strategy in CFRP and UNS A92024 aluminium sheet stacking with adhesive. A series of dry drilling tests have been developed with different cutting conditions and new noncoated WC-Co helical cutting tools. Analysis of Variance (ANOVA) statistical analyses and surface response models have been applied to determine the mechanical behaviour in the holes. For this purpose, the dimensional deviation, surface quality, and adhesive loss in the interface in relation to the number of holes have been considered. A combination of cutting parameters that minimizes the evaluated defects has been found. Diametric deviations and surface qualities below 2% and 3.5 µm have been measured in the materials that make up the stack with cutting speeds higher than 140 m/min and feed rates between 200 and 250 mm/min. However, the greatest adhesive losses occur at high cutting speeds.

Analysis of the drilling of the UNS A92024 alloy by cooling provided by biodegradable and low-cost vortex tube

In this work we have developed a low-cost and functional vortex tube model that can be manufactured with additive manufacturing techniques and an environmentally friendly material such as PLA. From the study of the available bibliography the geometry of the prototype has been defined. Its behaviour has been studied from CFD (Computational Fluid Dynamic) and experimental tests. Finally, the functionality of the prototype has been verified by the decrease in temperature during drilling tests.

Study of kerf features on CFRP/UNS A97075 stacks machined by AWJM

Thought it is proven by several authors that conventional machining causes several damages when a stack of composite material and metallic material is machined, few studies have been carried out about the possible alternatives. On this report, Abrasive Water Jet Machining (AWJM) is used to machine stacks of CFRP/UNS A97075 and UNS A97075/CFRP. Related machining aspect such as kerf taper and other AWJM features are analyzed over the machined materials. It is discussed the veracity of the usual way to evaluate Kerf Taper. Both Stereoscopic Optical Microscopy (SOM) and Scanning Electron Microscopy (SEM) techniques are applied along the evaluation. Finally, not delamination is detected however it is clear to say that depending on the configuration of the stack, transport and inclusion of CFRP in the UNS A97075 will appear, and abrasive particles will be found, to a greater or lesser extent.

Cutting speed and feed-rate influence on fatigue behavior of dry machined UNS A97075 alloy

Fatigue behavior takes a special relevance in manufacturing aeronautical parts due to safety reasons. Considering friendly environmental techniques, dry machining results in higher severe cutting conditions, which may negatively affect the part surface integrity, depending on cutting parameters values applied. In this sense, surface finish can be related to fatigue behavior. Notwithstanding, there is a lack of research that evaluates how cutting parameters affect fatigue life of aeronautical aluminum alloys, and their relationship with geometrical deviations. This work aims to analyze cutting speed and feed-rate influence on fatigue behavior of aeronautical aluminum alloy UNS A97075-T6 dry turned specimens. In order to do this, several rotating bar bending fatigue test have been carried out. Surface roughness have been also analyzed through the arithmetical mean roughness value (Ra) and the mean roughness depth (Rz). Results obtained seem to indicate that an increase of feed-rate and cutting speed negatively affects the fatigue life of the tested specimens, taking surface conditions a special influence in this behavior.

Tool Wear Mechanism in Cutting of Stack CFRP/UNS A97075

The aeronautics industry’s competitiveness has led to the need to increase productivity with one shot drilling (OSD) systems capable of drilling stacks of dissimilar materials (fibre/metal laminates, FML) in order to reduce riveting times. Among the materials that constitute the current aeronautical models, composite materials and aluminium (Al) and titanium (Ti) alloys stand out. These one-pass machining techniques produce high-quality holes, especially when all the elements that have to be joined are made of the same material. This work has followed a conventional OSD strategy and the same cutting conditions applied to CFRP (carbo-fibre-reinforced polymer), Al and CFRP/Al stacked sheets to know the wear mechanisms produced. With this purpose, results were obtained by using current specific techniques, such as microstructural analysis, monitoring of the shear forces and analysis of macrogeometric deviations. It has been determined that when these drilling techniques are applied under the same cutting conditions to stacks of materials of a different nature, the results of the wear mechanisms acting on the tool differ from those obtained when machining each material separately. This article presents a comparison between the effects of tool wear during dry drilling of CFRP and UNS A97075 plates separately and when machined as stacks.

Experimental Study for Improving the Repair of Magnesium–Aluminium Hybrid Parts by Turning Processes

One of the lightest metallic materials used in the aeronautics, aerospace, and automotive industries, among others, is magnesium, due to its excellent weight/strength ratio. Most parts used in these industries need to be made of materials that are rigid, strong, and lightweight, but sometimes the materials do not simultaneously satisfy all of the properties required. An alternative is to combine two or more materials, giving rise to a hybrid component that can satisfy a wider range of properties. The pieces machined in these industrial fields must satisfy stringent surface roughness requirements that conform to the design specifications. This work shows an experimental study to analyse the surface roughness reached in hybrid components made up of a base of magnesium alloy (UNS M11917) and two inserts of aluminium alloy (UNS A92024) obtained by turning. Its purpose is to determine the influence of the factors and their possible interactions on the response variable, the surface roughness Ra. The study is carried out using a design of experiments (DOE). A product of a full factorial 23 and a block of two factors 3 × 2 was selected. The factors identified as possible sources of variation of the surface roughness are: depth of cut, feed rate, spindle speed, type of tool, location with respect to the specimen (LRS), and location with respect to the insert (LRI). Data were analysed by means of the analysis of variance (ANOVA) method. The main conclusion is the possibility to carry out the repair and maintenance of parts of magnesium–aluminum hybrid components by dry turning; that is, without cutting fluids and, therefore, in the most sustainable way that the process can be carried out. In addition, different combinations of cutting parameters have been identified that allow these operations to be carried out in an efficient manner, reducing mechanization times and, therefore, also the direct and indirect costs associated with them.

Corrosion Resistance Evaluation and Effects of Prior Corrosion and Stress on Fatigue Behavior of Friction Stir Welded AA2024-T3

The corrosion resistance of 2024-T3 (UNS A92024) Al alloy with no clad layer and that of friction stir welded (FSW) joint specimens fabricated from the same material were evaluated. The surfaces of both the alloy base material and FSW joint specimens were ground out before being exposed to a 3.0% sodium chloride solution at 60°C for 24, 48, 72, or 96 h. The corrosion pits on the base material samples were found to be randomly distributed, while those on the FSW joint were formed around the edge and center of the weld line. Energy dispersive x-ray spectrometry indicated constituent particles containing Mg at the grain boundaries in the thermomechanically affected zone and stir zone of the FSW joint; this Mg content aggravated the corrosion damage in those regions. The depth and volume of the corrosion pits in the FSW joint were greater than those in the base material. However, the aspect ratios of the corrosion pits in the base material and FSW were similar. Prior-corroded specimens were fatigue tested to evaluate the effect of corrosion damage. The fatigue life of the base material with corrosion damage was slightly shorter than that of the FSW joint specimens with corrosion damage, and the fatigue life of an uncorroded FSW joint specimen was more than 10 times longer than that of a corroded specimen. Thus, corrosion damage has a severely detrimental effect on fatigue life. Further, fracture surface observation revealed that the fracture origins in the FSW joint specimens tended to be multiple corrosion pits; however, the corrosion pits with the greatest depth or volume did not necessarily become fracture origins in the base material or FSW joints.

Investigation of a Magnesium Oxide Primer Coating System on 2024-T351: Elucidation of Protection Mechanisms

Due to its high strength-to-weight ratio, aluminum alloy 2024-T351 (UNS A92024) is commonly employed in aircraft airframes for commercial and military application. The heterogeneous microstructure of this alloy makes it susceptible to localized corrosion in the form micro-galvanic coupling between the matrix and constituent particles1. Corrosion induced damage must be prevented with an actively protective coating system. For this reason, a Mg-rich primer (MgRP) coating was developed for the protection of 2024-T351. The MgRP system consists of an epoxy-based primer with metallic magnesium pigment and polyurethane-based topcoat applied over pretreated 2024-T3512-7 (Figure 1). The role and effect of pretreatment, MgRP, and topcoat on the coating’s performance has been the subject of several inquiries4-6 , 8 , 9. These studies show that the MgRP operates primarily via a sacrificial anode-based cathodic protection where 2024-T351 is protected from corrosion during Mg oxidation. However, additional protection mechanisms may operate as well such as beneficial coverage by Mg(II) corrosion products which chemically deposit onto remote scribe areas exposing the substrate. For this reason, the performance of a MgO-rich primer (MgORP) was also studied to assess chemical protection effects of stored and released Mg2+ (both in solution and as various corrosion products) as a source of chemical inhibition and to investigate its own merit as a reliable coating for corrosion protection (Figure 1). This investigation sought to determine the mechanisms of protection brought about by Mg-converted and MgO pigments towards artificial scratches in coatings on 2024-T351. It is hypothesized here that additional protection is afforded by Mg2+ in the form of aqueous ions and, perhaps more importantly, corrosion product. This hypothesis is tested by exploring local chemical conditions in scribes exposing 2024-T351 that arise as a result of the corrosion of MgRP or chemical dissolution of MgO. It merits comment that this hypothesis pertains to both MgORP and MgRP after which the Mg pigment has been converted to corrosion product from exposure. In order to examine the fate of Mg upon oxidation and how oxidized Mg affects the corrosion protection behavior of the coating system (both intact and with defects exposing the substrate), this investigation explored a Mg and MgO primer system in a variety of exposures. Coatings were tested in laboratory exposures such as Cycle Testing4 , 6 in 5 wt % NaCl and ASTM B-117 and also in marine and inland field exposure. X-ray Diffraction monitored the depletion of crystalline Mg and MgO and their conversion to crystalline corrosion products in the coating5-7 , 9. The quality of the primer and/or topcoat barrier was monitored with electrochemical impedance spectroscopy. Energy dispersive spectroscopy and Raman spectroscopy tracked Mg2+ migration from the primer towards an artificial scratch4-6 , 9. The amount of Mg in the scratch increased with exposure time. Moreover, Mg corrosion products (like Mg(OH)2) were deposited onto 2024-T351 substrate to explore how they impacted the corrosion behavior of bare 2024-T351 as assessed by electrochemical testing. From the results of this investigation, an explanation been proposed to rationalize how a MgO primer affords protection against corrosion of 2024-T351. This mechanism explains how MgORPs function towards corrosion protection and also why MgRP that has largely been depleted of Mg to form corrosion products (like Mg(OH)2, MgO, MgCO3) continues to protect the 2024-T351 substrate from corrosion. Validating this proposed mechanism will increase our understanding of the long-term protection behavior of spent MgRP and of MgORP coating systems. Figure 1

Experimental Parametric Model for Indirect Adhesion Wear Measurement in the Dry Turning of UNS A97075 (Al-Zn) Alloy.

In this work, the study of the influence of cutting parameters (cutting speed, feed, and depth of cut) on the tool wear used in in the dry turning of cylindrical bars of the UNS A97075 (Al-Zn) alloy, has been analyzed. In addition, a study of the physicochemical mechanisms of the secondary adhesion wear has been carried out. The behavior of this alloy, from the point of view of tool wear, has been compared to similar aeronautical aluminum alloys, such as the UNS A92024 (Al-Cu) alloy and UNS A97050 (Al-Zn) alloy. Furthermore, a first approach to the measurement of the 2D surface of the adhered material on the rake face of the tool has been conducted. Finally, a parametric model has been developed from the experimental results. This model allows predicting the intensity of the secondary adhesion wear as a function of the cutting parameters applied.