Potentiodynamic Polarization Tests Research Articles

Enhancing Corrosion Resistance of Q355B Steel in Marine Environments Using Graphene Doped Inorganic Zinc-Rich Coatings

Prolonged exposure of Q355B steel to the marine environment renders it susceptible to corrosion from seawater salt spray. In this study, inorganic zinc-rich coatings incorporating different components of graphene and calcium carbonate as anti-corrosion strategy were designed and aimed to improving their corrosion resistance. The anti-corrosion performance of these coating on Q355B was evaluated using scanning electron microscopy (SEM), X-ray diffraction (XRD), Potentiodynamic polarization tests and electrochemical impedance spectroscopy. Results indicated that the coating of 2G-1.5CaCO3-ZRC exhibited a corrosion current density of 1.565×10-5A·cm-2 and an impedance value of 734.6 Ω after immersion in simulated seawater solution for seven days. Compared with the untreated coating, this formulation demonstrated reduced corrosion current density and increased impedance values, indicating that the incorporation of graphene and calcium carbonate effectively mitigated corrosion rates while prolonging the materials protection duration. This work delivers the potential application in the field of protection for metal structures in seaport areas.

Role of surface grain refinement in AZ31 Mg alloy by shot peening on surface energy, biomineralization and degradation behavior

Grain refinement of magnesium (Mg) alloys to improve their performance as potential candidates for degradable implant applications is a promising strategy in the field of materials engineering. Surface properties play an important role in promoting higher implant tissue interactions which dictate the healing rate of the fractured bone. In the present work, AZ31 Mg alloy was subjected to shot peening by using steel balls of 2 mm diameter. From the microstructural studies carried out at the cross section, fine grain structure was observed up to 50 μm depth from the surface. Grain refinement up to ∼1.5 μm was achieved at the surface of shot peened AZ31. X-ray diffraction analysis confirms the development of non-basal texture at the surface. Increased surface energy was measured by contact angle measurements for the shot peened AZ31. Higher hardness was measured from the surface in the thickness direction of the AZ31 after shot peening. Corrosion behavior assessed by potentiodynamic polarization tests indicated marginally increased corrosion resistance for shot peened AZ31. In vitro bioactivity studies carried out in simulated body fluids demonstrated higher mineral depositions and lower weight loss for the surface grain refined AZ31. The results demonstrate the potential of shot peening to promote higher biomineralization and to control the degradation in improving the performance of biodegradable AZ31 Mg alloy.

EFFECT OF HEAT TREATMENT OVER THE MECHANICAL PROPERTIES AND THE RESISTANCE TO CORROSION OF THE TERNARY Cu-Al-Ag ALLOY

Abstract In the present work, the manufacture of a Cu-9Al-3Ag alloy was carried out easily through a green molding process. After dimensioning and slitting, the alloy samples were subjected to quenching, normalizing, and annealing heat treatments, to exert phase transformations that would, in return, aid into clarifying the influence of the phases present on the mechanical properties, such as hardness, as well as the behavior when exposed to a commonly known mildly corrosive media such as NaCl. The results obtained reveal an increase in hardness (assessed through either HRB) and (microhardness HV) in the quenched and annealed sample, as well as better corrosion resistance. The characterization was carried out through optical microscopy, Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), potentiodynamic polarization tests and electrochemical impedance spectroscopy.

Trade-Off Between Wear/Corrosion Performance and Mechanical Properties in D-AlNiCo Poly-Quasicrystals Through CNT Addition to the Microstructure

An ultrafine-grained Al71Ni14.5Co14.5/CNT poly-quasicrystal (QC/CNT) composite was synthesized using spark plasma sintering of powder components developed through electroless Ni-P/CNT plating of Co particles and mechanical alloying. The performance of the synthesized samples was studied using various testing methods, such as room temperature/hot compression, wear, and corrosion tests. The results were compared to the properties of alloy samples fabricated from raw and coated powders (without CNTs). The wear rate and friction coefficient of the quasicrystalline samples improved significantly due to the contribution of the CNTs. The wear rate of the CNT-containing specimens was 0.992 × 10−4 mm3/N/m, which is 47.1% lower than that of the QC sample. The positive impact of the CNTs on the corrosion potential and current density was further validated by the potentiodynamic polarization tests in a saline solution. However, these improvements in surface properties came at the cost of a 21.5% reduction in compressive strength, although the compressive strength still remained above 1.1 GPa at 600 °C. The results highlight an interesting trade-off between surface properties and mechanical strength, pointing toward the development of materials suitable for extreme conditions.

Corrosion Behavior of SLMed Ti6Al4V-Equine Bone Nanocomposites

Ti6Al4V is one of the most widely used Ti alloys in biomedical applications, such as orthopedic and dental implants, due to its excellent mechanical properties, biocompatibility, and high corrosion resistance. Metal implants require high bonding strength between the implant and bone for long-term use in the human body; Hydroxyapatite (HAp) has generally been used as it can be expected to provide high osseointegration. However, in this study, Equine Bone (EB), which is a biowaste with a similar chemical composition to HAp and is environmentally friendly, was used instead. Ti6Al4V and EB were mixed through ball milling and then fabricated into Ti6Al4V-0.05EB composites using Selective Laser Melting (SLM). During the SLM process, localized high thermal gradients and rapid cooling rates leads to high strength and low ductility, making it challenging to use as a biomaterial. To overcome these issues, heat treatment was performed at temperatures corresponding to the <i>β</i> phase transformation. Subsequently, to evaluate the corrosion behavior after implantation in the body, the corrosion resistance of the Ti6Al4V-0.05EB nanocomposites was assessed through potentiodynamic polarization tests in a 0.9% NaCl solution, which simulates the physiological environment of the human body. Additionally, the effects of EB addition and heat treatment temperature on the corrosion behavior were also observed.

CORROSION BEHAVIOUR OF ADVANCED COMPOSITES CONTAINING SURFACE MODIFIED SIC AS REINFORCEMENT

The interface structure, micro-voids, pits, delamination, intermetallic compounds and internal stresses are the utmost critical factors influencing the corrosion performance of composite materials making them unsuitable for use in structural applications. One useful technique to control such adverse effect in composites is surface modification of the reinforcement. The present investigation involved the implementation of chemical techniques, particularly electroless plating (EP), to modify the surface of silicon carbide (SiC) particles by depositing a layer of nickel phosphorous (Ni-P) onto them. These plated SiC particles were subsequently employed in the production of Al/Ni-pSiC composites using the powder metallurgy (PM) method, with different weight percentages of plated SiC content ranging from 5% to 15%. The corrosion behaviour was assessed by potentio-dynamic polarization tests in 3.5% NaCl solution at room temperature. Results confirmed that AlNi-pSiC composites exhibit a greater resistance to pitting, in contrast to pure aluminium and Al/SiC composites without plating. The enhanced corrosion resistance in Al/Ni-pSiC composites can be attributed to strong interfacial bond, grain refinement, CTE difference, formation of Ni3Al, and reduced potential difference.

One-step electrodeposition of reduced graphene oxide-amorphous carbon composite coatings for proton exchange membrane fuel cell bipolar plates

In this paper, a convenient electrodeposition method is proposed to directly fabricate a reduced graphene oxide-amorphous carbon composite coating (rGO-ACC) on a 316L stainless steel substrate. The rGO-ACC coating is achieved through a one-step reduction by utilizing a choline chloride-ethylene glycol deep eutectic solvent (DES) with the dispersion of graphene oxide. The analysis results from SEM, Raman and XPS reveal that the obtained rGO-ACC coating, with layered wrinkle morphology, uniformly covers and covalently bonds to 316L stainless steel substrate. Potentiodynamic and potentiostatic polarization tests showed that the corrosion current densities of rGO-ACC coated 316L stainless steel were of the order of 10-7 A cm−2 in simulated proton exchange membrane fuel cells (PEMFC) working environment, indicating a significant improvement of corrosion resistance of 316L and an excellent electrochemical stability. Meanwhile, compared with the naked 316L steel, the interfacial contact resistance (ICR) of the coated stainless steel is significantly reduced due to the outstanding electrical conductivity of the coated rGO. The results manifested that deposited rGO-ACC on steel surface may be a highly promising modification method for PEMFC metal bipolar plates.

Corrosion studies of Al-Mg-Sc-Zr Alloy with Low Sc/Zr ratio fabricated by laser powder bed fusion for marine environments

This study investigates the corrosion behavior of a laser powder bed fusion (LPBF) Al-Mg-Sc-Zr alloy with a Sc/Zr ratio of less than 1 in 3.5wt% NaCl solution. X-ray diffraction (XRD) analysis revealed the presence of an Al matrix with face-centered cubic (FCC) structure and the secondary phase Al3(Sc,Zr) with L12 crystal structure. Microstructural analysis indicated a bimodal grain size distribution with fine equiaxed and columnar grains influenced by thermal gradients and secondary phase Al3(Sc,Zr). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests in 3.5wt% NaCl solution demonstrated that the alloy exhibits a less negative corrosion potential (Ecorr) and lower corrosion current density (icorr) compared to other Al-Mg-Sc-Zr alloys with higher Sc/Zr ratios, indicating superior corrosion resistance. The enhanced performance is attributed to the fine grain structure and the formation of a stable protective oxide layer facilitated by the higher Zr content.

Effect of Natural Inhibitors on the Corrosion Properties of Grade 2 Titanium Alloy.

This study investigates the effects of natural inhibitors (pomegranate, algae, and tomato extracts) on the corrosion resistance of titanium (grade 2). To deepen understanding the inhibition mechanism, Molecular Dynamic (MD) and Monte Carlo (MC) simulations were employed to analyze adsorption behaviors and identify optimal adsorption sites on titanium oxide (TiO2) surfaces for compounds within the inhibitors. Results indicate non-flat adsorption orientations, with pomegranate peel extract components showing superior inhibition capabilities, attributed to the formation of strong O-H chemical bonds with the TiO2 surface. In the experimental part of the study Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PDP) were conducted. Two electrolytes were tested: a solution 3.5% NaCl and a solution 0.5 M NaOH. All the tests were performed with 5% of inhibitor and with the reference solution. Also, inhibition efficiency was calculated on the base of PDP tests. The study found that pomegranate extract can act as a good corrosion inhibitor for titanium alloy in aqueous solutions 0.5 M NaOH. This was demonstrated by the increase in the corrosion potential and impedance modulus and decrease in the corrosion current density after the addition of pomegranate extract to the solution. However, in a 3.5% NaCl solution, the efficacy of pomegranate extract was less pronounced, probably due to the high aggressivity of the electrolyte. Tomato and algae extract have instead shown very low inhibition effects in all the tested conditions.

Corrosion Resistance and Fracture Toughness of Cryogenic-Treated X153CrMoV12 Tool Steel

Abstract Cryogenic treatment can be employed as an additional heat treatment step for martensitic steels, particularly high-carbon and high-alloy tool steels, to improve their mechanical properties and wear resistance. This enhancement results from a transformation of retained austenite and precipitation of finely distributed secondary carbides. The present study examines the impact of a shallow cryogenic treatment, performed between the quenching and tempering processes, on the corrosion resistance and fracture toughness of cold work tool steel X153CrMoV12. The influence of the shallow cryogenic treatment was evaluated using potentiodynamic polarization test, salt spray tests and three-point bending tests in various hydrogen charging conditions. In addition, the microstructure and phase transformation of the tool steel were investigated using high-resolution scanning electron microscopy, X-ray diffraction and dilatometer tests. The results suggest that the shallow cryogenic treatment followed by a single tempering cycle can slightly enhance the corrosion resistance of the steel. More importantly, the shallow cryogenic treatment positively affects fracture toughness and reduces hydrogen susceptibility. It is discussed how these improvements in the properties of the X153CrMoV12 steel are linked to the microstructural changes induced by the shallow cryogenic treatment.

Electrochemical synthesis, physical properties and corrosion behavior of electropolymerized polyaniline films developed on 316L stainless steel

AbstractPolyaniline (PANI) films may be developed on metallic substrates by a variety of electrochemical techniques. In the present work, PANI films were electrodeposited on AISI 316L stainless steel substrates by cyclic voltammetry (CV), chronoamperometry (CA), and chronopotentiometry (CP) with the objective of comparing the efficacy of each method, based on the integrity of the developed films. Cyclic voltammetry and anodic polarization were used to determine optimal electrodeposition parameters for the development PANI films using the CA and CP methods. The structure and morphology of the coatings were characterized by scanning electron microscopy, energy‐dispersive x‐ray spectroscopy, Fourier‐transform infrared spectroscopy, and ultraviolet–visible spectroscopy. Among the evaluated techniques, CV led to the formation PANI films with the best homogeneity as well as the lowest number of defects, such as cracks or pores. Subsequently, the corrosion resistance of AISI 316L steels with and without PANI was compared in a physiological saline solution (0.9% NaCl). Potentiodynamic polarization tests indicated that the PANI‐coated samples exhibited lower corrosion current density values (0.012 vs. 0.018 μA/cm2) and lower passive current density values (0.04 vs. 0.06 μA/cm2) in comparison to the bare AISI 316L steel. Additionally, long‐term monitoring by electrochemical impedance spectroscopy revealed that PANI films consistently exhibited superior polarization resistance up to 32 days of exposure in the 0.9%NaCl solution (233,000 vs. 207,000 Ωcm2).

Corrosion behaviour of nitroxy-QPQ additively manufactured 17-4 PH steel on marine and nuclear reactor components

The study investigates the corrosion behavior of untreated and nitroxy QPQ treated 17-4 PH stainless steel under NaCl environments. Potentiodynamic polarization tests reveal that the nitroxy layer forms an oxide coating, leading to a passivation phase with gradually increasing current density. Oxidation at different temperatures shows variation in corrosion potential, with the lowest current density observed at 450 °C, indicating enhanced corrosion resistance. SEM images of untreated steel show severe crevice and pitting corrosion, whereas nitroxy QPQ treated surfaces exhibit reduced corrosion, with minimal disturbance at 450 °C. Elemental analysis confirms the formation of oxides and nitrides, with increased oxygen content in oxide layers and decreased nitrogen content due to the formation of chromium nitrides. The oxide layer, enriched with oxygen, nitrogen, and chromium, acts as a passive film, protecting against corrosion even in NaCl environments. Elemental mapping further illustrates the correlation between oxidation temperature and corrosion resistance, with higher temperatures resulting in reduced corrosion rates. The combined nitriding and oxidation process enhances corrosion resistance by forming a dense and adherent oxide layer, serving as a barrier against corrosive agents.

Functional properties of expanded austenite generated on AISI 316L by plasma nitrocarburizing using different active screen materials

Abstract This study investigates the functional properties of the expanded austenite layers generated on AISI 316L austenitic stainless steel resulting from active screen plasma nitrocarburizing using different active screen materials, i.e. steel or solid carbon. Treatments were conducted at 460 °C for 5 hours in a nitrogen-hydrogen feed gas, whereas for the treatments using a steel active screen, methane was added as carbon precursor. Additionally, the bias plasma conditions applied at the samples were varied between 0 kW and 1.25 kW. Samples were characterized by complementary microstructural and compositional investigations, surface roughness and hardness measurements, pin-on-disk tribological tests as well as potentiodynamic polarization tests in H2SO4 and NaCl electrolytes. The functional properties of the case are discussed based on the contents of nitrogen and carbon in the expanded austenite and on their effective diffusion depths. The results show that the usage of a carbon screen generally produces surfaces with uniform layer thickness, high hardness, improved wear resistance and a delayed tendency to pitting corrosion independent of the bias condition applied to the samples. When applying both screen materials at non-biased condition, the general corrosion resistance is slightly reduced under the conditions used, however, the layers generated using the carbon screen have a wear rate that is 3 times lower. It can be concluded that the carbon screen represents a robust treatment variant for austenitic stainless steels to produce sufficiently thick and wear-resistant surface layers in a short treatment duration, which still have the potential to maintain the corrosion resistance in different environments.

Corrosion inhibition performance of protein derived carbon quantum dots as corrosion inhibitors on low carbon steel in sulfuric acid solution

Protein derived carbon quantum dots (PCQDs) were successfully fabricated via a hydrothermal method with shrimp meat as the precursor. Subsequently, their corrosion-inhibiting performance on mild steel (L-steel) in a 0.5 mol/L H2SO4 solution was evaluated. Electrochemical impedance spectroscopy (EIS) tests demonstrated that at a concentration of 250 mg/L, the corrosion inhibition efficiency of PCQDs exceeded 90 %. Potentiodynamic polarization (PDP) tests indicated that when the concentration of PCQDs reached 500 mg/L, the corrosion inhibition efficiency was as high as 97.45 %. Comprehensive characterizations of the PCQDs, including X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and ultraviolet–visible spectroscopy (UV–Vis), verified the existence of functional groups such as carboxyl, hydroxyl, and aromatic rings within the PCQDs. These groups are conducive to forming a strong adsorption force on the surface of L-steel and creating a protective layer. Surface morphology analyses carried out by scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that the surface of L-steel treated with PCQDs was significantly smoother in comparison to untreated samples exposed to acidic conditions. Adsorption studies disclosed a mixed physical and chemical adsorption behavior, and theoretical calculations showed that the N and S atoms in PCQDs preferentially adsorb in a parallel direction. The addition of PCQDs led to a reduction in the diffusion coefficient, indicating that the diffusion of corrosive ions was effectively hindered. The distribution function of PCQDs was 3.48 Å, which suggested that the chemisorption mechanism played a dominant role in the inhibition process.

Plasma electrolytic oxidation deposited HAp-Ta2O5 composite coatings on Ti6Al4V for biomedical applications: The importance of Ta2O5 reinforcing phase

In this research, the focus was placed on enhancing the properties of hydroxyapatite (HAp) coating by the addition of various concentrations of tantalum pentoxide (Ta2O5) nanoparticles, ranging from 0 to 1.5 g/L, to its electrolyte solution. The HAp-Ta2O5 composite coatings were deposited on the Ti6Al4V metallic implant using the plasma electrolytic oxidation technique. The results of the X-ray diffraction test indicated that the increased concentration of Ta2O5 nanoparticles has no significant effect on the phase composition of the coatings. The denser and rougher coatings were fabricated when 1.5 g/L of Ta2O5 nanoparticles were added to the solution. The favorable microstructural properties of the HAp-1.5 g/L Ta2O5 composite coating resulted in a notable improvement in the mechanical properties, i.e., >40% increase in both microhardness and bonding strength compared to HAp. The corrosion resistance of the coated implants was evaluated through electrochemical impedance spectroscopy and potentiodynamic polarization tests. The inclusion of Ta2O5 nanoparticles in HAp coating led to a 72% reduction in the corrosion current density of HAp, indicating the constructive contribution of the nanoparticles to improved corrosion protection. The samples were incubated in simulated body fluid for 7 days to assess their in vitro immersion performance. All of the PEO-derived coatings stimulated the nucleation and growth of apatite grains, showing their superior biomineralization ability. An obvious decrease in the level of harmful ions such as Al3+ and V5+ released from the surface of composite coatings was obtained. These findings suggest that the developed system has potential for dental and orthopedic applications.

Surface Engineering of Ti6Al4V: Impact of Rhenium–Carbon Coatings with Molybdenum Anchors on Biocompatibility and Corrosion Behavior

Titanium alloys, particularly Ti6Al4V, are widely used in biomedical applications due to their excellent mechanical properties and inherent biocompatibility. However, enhancing their surface characteristics, such as biocompatibility and corrosion resistance, remains a key challenge for their long-term use in medical implants. In this study, we investigate the effects of rhenium–carbon coatings deposited on Ti6Al4V substrates via magnetron sputtering, incorporating a molybdenum anchoring layer. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) analyses confirmed the formation of rhenium carbides, elemental rhenium, and rhenium oxides within the coatings. Despite these successful depositions, scanning electron microscopy (SEM) revealed significant delamination and poor adhesion of the coatings to the Ti6Al4V substrates. Corrosion resistance, evaluated through potentiodynamic polarization tests, showed an increase in corrosion current densities and more negative corrosion potentials, indicating a detrimental effect on the substrate’s corrosion resistance. Biocompatibility assessments using PK15 cells demonstrated a marked decrease in cell viability and metabolic activity, particularly in samples with higher surface roughness. These findings underscore the critical need for the optimization of surface preparation and deposition processes to improve both the adhesion and biocompatibility of rhenium–carbon coatings on Ti6Al4V substrates. Future research should aim to refine coating technique to enhance adhesion, explore the mechanisms of cytotoxicity related to surface roughness, and expand biocompatibility studies across different cell lines and biological environments.

Research on the corrosion protection of in-situ prepared Li[sbnd]Al layered double hydroxides on AZ31 Mg alloy under standard atmospheric pressure and low temperature

This work successfully prepared LiAl LDHs coatings on AZ31 Mg alloy under standard atmospheric pressure and low temperature. The whole process did not require a hydrothermal autoclave reactor and high pressure. Electrochemical test results showed that the coating was able to provide good corrosion protection performance. The LiAl LDHs coatings provided a large low-frequency impedance on AZ31. When the treatment time was 24 h, the maximum |Z|0.01Hz at pH = 12 was 5.14 × 104 Ω∙cm2, which is more than an order of magnitude higher than the |Z|0.01Hz of 1.81 × 103 Ω∙cm2 for the bare sample. Under the same treatment conditions, the potentiodynamic polarization test results showed that the LiAl LDHs coated samples had a lower corrosion current density and a higher breakdown potential. The icorr was 1.78 × 10−7 A/cm2 and Ebr was −0.82 VSCE compared to the Mg substrate (icorr of 1.13 × 10−5 A/cm2 and Ebr of −1.53 VSCE). Additionally, LiAl LDHs coatings also had a significant inhibitory effect on cathodic hydrogen evolution, providing targeted protection to the cathodic areas.

Development and characterization of corrosion-resistant plasma-sprayed Ni-Al composite coatings via graphene oxide fillers

In this study, the authors propose a procedure to enhance pure Ni-Al powders through graphene oxide dispersion in water for plasma spraying. The enhanced powders were utilized to coat A36 steel via plasma spraying. Next, the powders and the coatings were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, micro-Raman spectroscopy, and field emission scanning electron microscopy. Given the capability of the generated X-ray to characterize near surfaces to a depth of a few micrometers, the performed X-ray microanalyses convey that the carbon species incorporated within the powders through the graphene oxide dispersion can act as nanofillers reducing the number of holes/pores in the plasma-sprayed coatings. Potentiodynamic polarization testing and electrochemical impedance spectroscopy were used to investigate the corrosion behavior of the samples at two intervals: after 1 h and after 30 days of exposure to a 3.5 % NaCl solution. According to the results of the corrosion testing, the enhanced coatings can display about 2.35 times lower corrosion current density compared to pure Ni-Al coatings, with the corrosion potentials of the enhanced coatings being higher than that of pure Ni-Al coatings (i.e., improved corrosion resistance). This improvement in corrosion resistance is also evident when the enhanced coatings are compared to the A36 substrate after 30 days of exposure to the solution. It appears that the incorporated carbon nanofillers, by reducing deep holes and pores that communicate with the surface of the substrate, ultimately determine the highest corrosion resistance. Thus, the outcome offers enhanced Ni-Al coatings possessing superior anticorrosion properties that typical plasma-sprayed Ni-Al bond coats may not exhibit.

Impacts of T6 heat treatment on the microstructural, mechanical, and corrosion properties of thixoformed AA7075 alloy produced by cooling slope casting

Abstract Research into semi-solid metal forming techniques has been ongoing for an extended period with the aim of producing near-net shape products from aluminum alloys. The primary focus has traditionally been on casting alloys seeking to offer an alternative to the other processes such as high pressure die casting. Over the past twenty years, wrought aluminum alloys have also been explored for thixoforming operations as an alternative to traditional plastic deformation techniques. This research investigated the impacts of T6 heat treatment on the microstructural, mechanical, and corrosion properties of AA7075 alloy samples produced through cooling slope casting and subsequent thixoforming with different reheating durations. The selected alloy was chosen due to its widespread use in various industries, attributed to its excellent strength-to-density ratio achieved after T6 heat treatment. Building on optimized cooling slope casting parameters from a prior study, the standard solution treatment procedure following thixoforming with extended reheating times was found to be inadequate. Hardness and tensile tests revealed that specimens reheated for 120 min exhibited significantly reduced response to T6 treatment. Despite achieving the targeted hardness value of 154 HB with samples reheated for 20 min prior to thixoforming and T6 heat treatment, especially the elongation at break values were unsatisfactory. Potentiodynamic polarization tests indicated that corrosion primarily involved grain dissolution, with longer reheating times decreasing corrosion resistance due to increased amount of secondary phases and grain isolation. These findings highlight that while AA7075 alloy can be processed into semi-solid formable materials via cooling slope casting, issues such as hot tearing, micro-shrinkage, and physical defects post-thixoforming hinder the achievement of desired tensile properties.

Microstructural evolution and corrosion behavior of non-isothermally heat treated hypoeutectic Al-Si-Cu alloy

In the present work the effect of non-isothermal heat treatments on the microstructure and corrosion resistance of a hypoeutectic Al-Si-Cu die-cast alloy was studied. The microstructural aspects were examined by confocal laser scanning microscopy and scanning electron microscopy. The corrosion behavior was studied by potentiodynamic polarization tests. In the as-cast condition, the microstructure consisted of needle-like Si particles and Fe-rich intermetallics, besides the Al matrix. The non-isothermal treatments promoted spheroidization of Si particles, decreasing its volume fraction. The corrosion resistance was affected by concentration of the Si particles. The corrosion mechanism is discussed based on the microstructural evolution of the Al-Si-Cu alloy. The main influencing factor was the volume fraction of Si particles. The non-isothermally treated samples exhibited lower corrosion current density than the as-cast alloy, showing superior corrosion resistance.