Al-4 Wt Research Articles

Effect of friction stir processing on grain refinement and superplastic properties of binary Al-8 wt.% Si to Al-30 wt.% Si alloys

ABSTRACT As-cast binary Al–Si alloys containing ∼8, 12, 20, and 30 wt.% Si, representing the hypoeutectic, eutectic (12 wt.% Si), and hypereutectic compositions, were subjected to severe plastic deformation by friction stir processing (FSP) for grain refinement to 2.3–2.7 μm by dynamic recrystallization. Tensile tests conducted by differential strain rate test technique over the strain rates of 10−4 – 10−2 s−1 and test temperatures in the range of ∼840–530 K led to strain rate sensitivity index (m) varying from ∼0.04 to 0.40 depending on temperature, strain rate, and alloy composition. The constant initial strain rate tests conducted at 10−4 s−1 and 840 K exhibited a maximum elongation of 250% in the hypereutectic Al–20Si alloy, but the same increased linearly with m irrespective of alloy composition. Generally, with increasing Si content, the activation energy for deformation increased from 104.7 ± 14.4 kJ/mol for eutectic Al–12Si to 310.4 ± 32.3 kJ/mol for hypereutectic Al–30Si, which increased further to 572 ± 148 kJ/mol over the higher temperature range of 840–800 K. Analysis of observed deformation and microstructure behaviour supports the occurrence of superplasticity, whereby the accommodation of grain boundary sliding by grain boundary migration led to enhanced grain growth or else the local high-stress concentration at the particle-matrix interface led to cavity formation. There was no evidence of dynamic recrystallization during high-temperature tensile deformation but the flow softening observed is ascribed to the occurrence of concurrent cavitation.

Drimia maritima as a New Green Inhibitor for Al-Si Alloy, SAE Steel and Pure Al Samples in 0.5 M NaCl Solution: Polarization and Electrochemical Impedance Analyses

The corrosion inhibition effects of Drimia maritima (L.) Stearn sin. Urginea maritima (L.) Backer on three different materials, i.e., as-cast Al-7 wt.% Si alloy, SAE 1020 low carbon steel, and commercially pure Al samples, into a stagnant and naturally aerated 0.5 M NaCl solution are evaluated. For this purpose, both the potentiodynamic polarization curves and electrochemical impedance spectroscopy with an equivalent circuit are utilized. It is found that inhibition effect increases up to certain minor Drimia maritima content. Adsorption isotherms (e.g., Langmuir and Temkin) indicate that all three examined materials comprise physical adsorption mechanisms. Al-Si alloys attained inhibition efficiencies of about 96% at 25 °C with 1250 ppm of Drimia maritima and ~43% with 625 ppm at 45 °C. On the other hand, the cp. Al and SAE 1020 samples attain ~89% and 68% with 1250 ppm and 500 ppm at 25 °C, respectively. This clearly indicates that the dosage of Drimia maritima green inhibitor into NaCl solution possesses certain susceptibility for each distinctive material examined. Impedance parameters obtained by using CNLS (complex non-linear least squares simulations) are correlated and discussed.

Nano-twinned silicon in Al-Si alloys for high wear-resistance

Wear-failure is the most common damage for power transmission components in the field of engineering materials, constituting approximately one-fourth in service loss. The development of high wear-resistant Al alloys plays a crucial role in reducing energy demand and weight, and then attributes to the achievement of dual-carbon target. Here we report a novel strategy to develop outstanding wear-resistant (the coefficient of friction of 0.31) Al-10 wt%Si alloys at room temperature, based on the formation of multiple parallel {111} twins and hierarchical {111}-{111} double twins by a route of combining ultrahigh pressure solid solution and electropulsing assisted aging (HPEP), which overwhelms all values of Al alloys, even Ti alloys and high entropy alloys reported so far. The microstructure, formation process and wear-resistant mechanism of nano-twinned Si have been clarified by transmission electron microscopy observations, molecule dynamics simulations and the first principles calculations. It demonstrates that the interactive nano-twinned Si structures are mainly introduced through twin-twin collision or the phase/matrix interface prohibition of twin motion, which are effective to restrain atom separation in contrast to eutectic Si perfect crystal, resulting in homogeneous wear-loss and long operation life. Those new results provide insights towards designing wear-resistant materials with high mechanical properties.

Effect of Y2O3 on thermophysical parameters and mechanical properties of Al-Al2O3 composites and compatibility with high temperature Al-Si alloys

Abstract Al-Al2O3 is a crucial encapsulation composite used in solar thermal storage systems. This study utilized Al and Al2O3 powders as raw materials, with Y2O3 serving as a sintering aid, to prepare Al-20Al2O3-xY2O3 composites (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0 wt%) through the cold pressure sintering method. The latent heat, thermal conductivity, and bending strength of the Al-20Al2O3-xY2O3 composites were measured. The compatibility of the composites with Al-12 wt%Si alloys was analyzed. Furthermore, the relationships between thermophysical parameters, mechanical properties, compatibility, and microstructure were explored. The oxidation mechanism of Al and the wetting angle of the composites with Al-12Si were simulated using LAMMPS software. It was concluded that with an increase in Y2O3 content, the bending strength, thermal conductivity, and compatibility of the composites initially increased and then decreased. The Al-20Al2O3-0.2Y2O3 composite exhibited the least porosity, highest bending strength (76.32 MPa), and thermal conductivity (46.82 W/(m·K)). In compatibility testing, the diffusion distance of Si atoms was shortest (90 μm) in the Al-20Al2O3-0.2Y2O3 composite. Moreover, this composite had the largest wetting angle (88°) with the Al-12Si alloy, resulting in good compatibility between them.

Influence of Mg Content on Microstructure Coarsening, Molten Pool Size, and Hardness of Laser Remelted Al(-x)-Mg-Sc Alloys.

Investigations leading to high-quality surfaces and optimized properties in laser remelted Al-Mg-Sc alloys remain scarce. Laser surface remelting (LSR) has been used for the final treatment of these alloys processed through additive manufacturing. However, the direct microstructure responses of the treated cast surfaces have not yet been investigated. In the present research, Al-3, 5, and 10 wt %-Mg-0.1 wt %-Sc alloys plates were processed using LSR to study the effects of local melting and rapid solidification. The morphology of the α-Al phase, microstructure coarsening, and hardness were mapped from the bottom to the top of the molten pools, varying with local Mg content and laser heat input (2.5 J/mm, 5 J/mm, and 10 J/mm). This study aimed to create a comprehensive map of the microstructures, hardness, and molten pool sizes under various conditions. The findings may help to optimize these alloys through understanding laser processing parameters. Methods used included CALPHAD computations, optical microscopy, SEM, EDS, image analysis, hardness tests, and heat flow models. The results obtained showed α-Al cell growth with bands in all alloys with hardness changes correlating with cell spacing and heat input. Higher Mg content resulted in more refined cells and a higher fraction of bands. Increased Mg content decreased the thermal diffusivity and enthalpy of melting, enlarging the molten pool size. Hardness increased with decreasing heat input and higher Mg content in the tested alloys, especially in the Al-10 wt %-Mg-0.1 wt %-Sc alloy as the heat input was varied.

Cellular automata-lattice Boltzmann model for polycrystalline solidification with motion of numerous dendrites

A GPU-accelerated cellular automata-lattice Boltzmann combinatorial model is developed for calculating the preferred growth, movement, and collision behavior of equiaxed crystals in supercooled melts of binary alloys. For moving dendrites, the growth is computed in a dynamic grid that grows with the body, and continuous movement is achieved by moving the dynamic grid. The impulse-based method is used for the collision of dendrites to calculate the post-collision velocity. Each module of the model was rigorously benchmarked, proving that the model has good computational accuracy and efficiency. The model was used for modeling the solidification of an Al-3 wt% Cu alloy, simulating the growth of abundant kinematic equiaxed crystals in a rotating flow and the falling and stacking of dendrites in droves and subsequent grain growth during the columnar to equiaxed transition, respectively.

Localized Corrosion Behavior and Corrosion Microstructure of LZ91 and LAZ931 Mg Alloys

LZ91 (Mg-9 wt%Li-1 wt%Zn) and LAZ931 (Mg-9 wt%Li-3 wt%Al-1 wt%Zn) alloys are emerging ultra-lightweight Mg alloys, which can be used in applications that require weight reduction. Although LZ91 alloy has found some success in the 3C industry, the relatively inferior mechanical strength limits its widespread application. To improve the mechanical properties, Al was added to LZ91 alloy to form LAZ931 alloy. However, both LZ91 and LAZ931 alloys are primarily composed of a dual-phase structure with α (HCP) and β (BCC) phases, which form a microgalvanic couple in the corrosion environment. Furthermore, adding Al introduces additional secondary phases, such as AlLi and MgLi2Al, which complicate the corrosion behavior and mechanism. Therefore, this study investigates the corrosion behavior and microstructure of LZ91 and LAZ931 Mg alloys in 3.5 wt% NaCl solution and the relationships to the phase distribution in the alloy substrates.By in situ optical microscope (OM) observations and open circuit potential (OCP) monitoring, localized corrosion initiates on the LAZ931 alloy earlier than on the LZ91 alloy. The early initiation and propagation of localized corrosion on the LAZ931 alloy result in worse corrosion resistances and faster corrosion rates measured by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. By scanning Kelvin probe force microscopy (SKPFM), the Li-rich β phase is more active than the Mg-rich α phase. However, interestingly, localized corrosion was found to preferentially propagate inside the α phase, which seems to contradict the SKPFM measurements. The preferential propagation of localized corrosion in the α phase could be related to the difference in the surface corrosion film thicknesses on the α and β phases before localized corrosion propagation. The localized corrosion behavior and corrosion microstructure of the alloys will be discussed based on electrochemical measurements and site-specific microstructure characterizations. Figure 1

Effect of SiC content on the microstructure and wear behavior of cold-sprayed Al-SiC coatings deposited on AZ31 alloy substrate

As a promising and recently developed deposition technique, cold spray deposition method is among the most recently implemented approaches to enhance the poor hardness and wear resistance of AZ31B magnesium alloy. This study investigated the effect of SiC content on the microstructural characteristics, microhardness, and wear behavior of cold-sprayed Al-(16, 28, and 38 wt%) SiC composite coatings. The incorporation of SiC particles into the Al-matrix coating led to the development of a mechanical interlocking mechanism and improved coating-substrate interfacial bonding. The microhardness of the Al-38 wt% SiC coating was approximately 80 % higher than that of the bare substrate due to reduced porosity and a uniform distribution of SiC particles. For coatings with higher SiC content, the dominant wear mechanism transitioned from adhesive to abrasive wear, as evidenced by the friction coefficient (COF) values and wear track micromorphology. The Al-16 wt% SiC coating exhibited the lowest COF and wear rate values, indicating superior wear resistance among the specimens.

Effects of external static electrical field on thermal and electrical conductivity in the Al-Cu, Al-Ni, and Al-Si eutectic alloys

This study aims to investigate the effects of external positive and negative static electric fields (E+ and E- respectively) on thermal conductivity (K) and electrical conductivity (σ) in Al-33 wt. % Cu, Al-6.4 wt. % Ni and Al-12 wt. % Si eutectic alloys. For this purpose, the solidifications of Al-Cu, Al-Ni, and Al-Si eutectic alloys were directionally done under E+ and E-. The directions of E were chosen to be parallel (E+) and antiparallel (E-) to the solid-liquid (S-L) growth direction and the magnitudes of E were approximately (+10) and (−10) kV cm−1 and (+16) and (-16) kV cm−1 for the Al-Cu, Al-Ni, and Al-Si eutectic alloys, respectively. The effects of E+ and E− on the K and σ were determined by the longitudinal heat flow and the four-point probe methods, respectively. While the K and σ values decreased with increasing temperature, the K and σ were increased and decreased with E+ and E−, respectively.

Simultaneous enhancement of strength and ductility in Al-Zn-Cu casting alloy with trace Mg addition designed by first principle calculation

The Al alloy containing 17 wt% Zn exhibits enhanced strength through Zn precipitation after casting without the need for further aging treatment. DFT (Density Functional Theory) calculations revealed that the addition of Cu and Mg elements to Al-Zn alloy has the potential to stabilize the Zn phase in the Al matrix and reduce the interface energy between the Zn precipitate and Al matrix. Based on these findings, 0.5 wt% Cu and 0.1 wt% Mg were added to the Al-17 wt% Zn alloy. The trace element level of 0.1 wt% Mg addition led to a significant increase in both yield and tensile strength, from 132 to 278 and from 248 to 310 MPa, respectively, compared to the Al-17 wt% Zn alloy with 0.5 wt% Cu. Furthermore, their ductility surpassed 11 %. The trace amount of Mg greatly increased yield and tensile strength, while Cu enhanced the ductility in the Al-Zn alloy after casting without any aging treatment.

Tribo-mechanical performance of Al-nano TiC composites processed by microwave-assisted powder metallurgy

This study aims to investigate the microstructural, mechanical, and tribological characteristics of Al-nano TiC composites. The microwave-sintered nanocomposites were analyzed using optical and scanning electron microscopes, providing valuable insights into the spatial distribution and interaction of TiC within the matrix material. Microstructure characterization confirmed the uniform dispersion of nano TiC particles throughout the Al. Furthermore, the microwave-sintered nanocomposite samples displayed greater hardness than pure aluminum, indicating the strengthening impact of nano-TiC. Al-6 wt.% nanocomposites fabricated using microwave-sintered powder metallurgy showcased an impressive hardness rating of 51 VHN. The assessment of tribological properties revealed that a higher TiC concentration reduced wear rate, showcasing improved surface protection. However, it was observed that the friction coefficient rise with the addition of nano-TiC particles, implying changes in the bonding between the composite and the interacting surface. The thorough examination of worn surfaces yielded insights into the wear mechanisms present in the nanocomposite materials. Detailed examination of worn surfaces highlighted the formation of protective oxide layers, contributing to the improved wear resistance. This research contributes to our understanding of the complex interactions occurring during tribological processes by clarifying the morphological features of worn surfaces.

Deformability, inherent mechanical properties and chemical bonding of Al11Nd3 in Al-Nd target material

Microstructure uniformity of the Al-Nd target materials with Al11Nd3 significantly affects the performance of the fabricated Al-Nd film, which is widely used as wiring material in large-size thin-film transistor liquid crystal display (TFT-LCD) panels. Understanding the inherent mechanical properties and chemical bonds of Al11Nd3 is crucial for homogenizing the Al-Nd target. Here, by a combined experimental and ab-initio theoretical study, the microstructure and deformability of the Al-3wt%Nd alloy and the inherent mechanical properties and chemical bonds of Al11Nd3 were investigated comprehensively. The Al-3wt%Nd alloy is composed of the pre-eutectic α-Al matrix and the eutectic α-Al and a high stable α-Al11Nd3 phase. During the plastic deformation, the eutectic microstructure transforms from a cellular to a lamellar shape, while the morphology and dimension of α-Al11Nd3 are not changed significantly. By examining ideal tensile strength, elastic moduli, hardness and brittleness-ductility, the hardness-brittleness of α-Al11Nd3 is quantitatively evaluated, accounting for its difficulties of plastic deformation and fragmentation. Combining band structure, population analysis, topological analysis and crystal orbital Hamilton population, we found that α-Al11Nd3 possesses two types of chemical bonds: the Nd-Al and Al-Al bonds. The former is a typical ionic bond with electron transfer from Nd to Al, while the latter, dominated by both 3s-3p and 3p-3p interactions, is a weak covalent bond. The mixed chemical bond is responsible for the high hardness-brittleness of α-Al11Nd3. This work is expected to lay a foundation for Al-Nd alloy and catalyze the fabrication of high-quality Al-Nd target materials.

Growth Behaviors of Bubbles and Intermetallic Compounds in Solidifying Al-5 wt.% Mn Alloy

The growth behaviors of hydrogen bubbles and intermetallic compounds (IMCs) during solidification of an Al-5 wt.% Mn alloy was investigated by synchrotron radiography. Results show that bubble collapse can increase hydrogen concentration in nearby Al melt, thus facilitating the formation and growth of new bubbles. Under the interference of Al6Mn IMCs, the growth method of an individual bubble is changed from a Gaussian distribution to a linear model. Al6Mn crystal growth can be divided into three stages: first an isotropic spherical crystal appears, then it evolves into primary branches, and eventually forms an irregular octahedron.

Impact of cooling rates on the microstructure and cracking susceptibility of hot-dip galvanized Zn-12 wt% Al-5 wt% Mg coatings

Zinc-Aluminum-Magnesium (ZnAlMg) alloy coatings, applied through the hot-dip galvanizing process, are renowned for their superior corrosion resistance. This study investigated how different cooling rates affect the microstructure and cracking tendency of Zn-12Al-5Mg (in wt%) coatings. It was found that faster cooling rates lead to a more refined microstructure with primary MgZn2 grains but also increase the likelihood of cracking. This is primarily attributed to the finer distribution of primary MgZn2 grains and ternary eutectic (Zn/MgZn2/Al) regions, which allows micro-cracks originating from hard and brittle MgZn2 grains to easily propagate through the surrounding eutectic regions and develop into macro-cracks. Notably, we observed an epitaxial relationship between the primary and binary eutectic MgZn2 phases, shedding light on their crystallographic orientation and morphology. Additionally, our investigation revealed that cracking susceptibility depends on the crystallographic orientation of MgZn2 grains relative to the tensile axis. Fiber-like MgZn2 grains tend to crack along their basal planes, while hexagonal grains crack along other crystallographic planes. This insight into cracking behavior is crucial for designing ZnAlMg coatings with enhanced corrosion resistance and mechanical integrity. Overall, while faster cooling rates refine the microstructure, they can also increase the susceptibility to cracking in ZnAlMg coatings with Mg contents exceeding 3 wt%, emphasizing the need for a balanced approach in optimizing coating properties for different applications.

Influence of Si on the thermal expansion behavior and photo-electrochemical protection of Al-13 wt.% Si binary casting alloy

Influence of Si on the thermal expansion behavior and photo-electrochemical protection of Al-13 wt.% Si binary casting alloy

Solidification paths of Al-Cu-Sn alloys: Comparison of thermodynamic analyses and solidification experiments using in situ X-radiography

The increasing importance of Al-Cu-Sn alloys as materials for producing self-lubricating bearing materials in automotive industries requires the development of uniform microstructures with improved performance, which could be achieved by a precise control of solidification processes. Adding Sn to Al-Cu binary alloy could dramatically alters the solidification path, generating liquid phase separation and monotectic reaction. In this paper, Al-10 wt% Cu-X wt% Sn (with X = 0; 5; 10 and 20) alloys have their solidification paths investigated by three different complementary approaches. Firstly, the solidification paths were calculated by using the CALPHAD method through Thermo-Calc software revealing the sequence of transformations that could occur during the solidification of these alloys, from the formation of the initial α-Al dendrites to the final eutectic reaction. Secondly, experimental thermal analysis was carried out by DSC (Differential Scanning Calorimetry), which reveals the successive events that occur during the controlled melting and cooling of these alloys. Thirdly, directional solidification was performed on all alloys, with in situ and real-time observations achieved through the utilization of X-radiography. The comparison between the various approaches showed a suitable correspondence between the history of the alloy solidifications computed by Thermo-Calc and those obtained experimentally (DSC and directional solidification experiments). Additional information about the dynamics of each reaction was obtained during the directional solidification experiments in terms of microstructures, segregation, and the genesis of the liquid phase separation that occurred for high Sn-content alloys.

Development of a novel processing technique for cold-rolled Al-3 Mg aluminum alloys via athermally-enhanced electrical annealing

In this study, we proposed an alternative to the conventional warm forming processing for the softening of hard cold-rolled Al-3 wt% Mg aluminum alloys to improve formability. A novel processing technique was proposed via athermally-enhanced electrical annealing. The softening of the aluminum alloy to a maximum 48.2 % micro-hardness decrement at 158.5 °C was achieved via current-induced recrystallization at 4.0 × 104 A/cm2 and above for 1 h, as evidenced by the formation of strain-free equiaxial grains, the release of accumulated residual stress, the transformation of subboundaries and low-angle grain boundaries to high-angle grain boundaries, and the transformation of deformation texture to recrystallization texture. This study aims to provide a sustainable processing technique for the circular economy to achieve lower annealing temperature and energy consumption.

Experimental investigations with machine learning techniques for understanding of erosion wear in advanced aluminum nanocomposites

This article addresses the significant challenge of erosion wear in aluminum composites, particularly in industries such as automotive, aerospace and energy, where sustained material performance is crucial. The study focuses on the experimental investigation of erosive wear characteristics exhibited by advanced aluminum nanocomposites, utilizing an air jet erosion wear test apparatus. The erosion wear tests were conducted using diverse parameters, such as angles (30°, 45°, 60° and 90°), air pressures (1–4 bar) and a fixed 600-s duration, maintaining a constant sand particle feed rate of 2.0 (g/min) and utilizing stand-off distances of 10, 15 and 20 mm. Surface assessments were conducted using field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS). The results revealed observable specimen wear, particularly at a 45° angle, with wear rates decreasing at higher impingement angles and reaching a minimum at 90°. Notably, the Al-4 wt.%TiC nanocomposites exhibited a 25% improvement in wear resistance compared to the base alloy. Further analysis of eroded surfaces through (FE-SEM) revealed a mechanism involving micro-cutting, plowing and grain pull-out, attributing wear primarily to plastic deformation and crack formation. Evaluating erosive wear results through six machine learning (ML) models demonstrated that gradient boosting regression emerged as the most accurate, achieving an R2 value of 0.97. This highlights the effectiveness of ML in predicting erosion wear rates and offers insights for improving aluminum composite materials in demanding industrial applications.

Corrosion behaviors of single-layer and double-layer nickel alloy coatings fabricated by arc spraying and high-velocity oxy-fuel

This study investigates single-layer and double-layer thermally sprayed nickel alloy coatings (bond and top coatings). Ni-5 wt% Al and Ni-20 wt% Cr were used as bond coatings, whereas highly alloyed Ni-based coatings, Hastelloy C276 or Inconel 625 were used as top coatings. Arc spraying (A) and high-velocity oxy-fuel (HVOF) techniques were used to create the coatings on a 304 stainless steel substrate. The samples were studied by performing potentiodynamic polarization tests in a 20 vol% H2SO4 solution at room temperature. The scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) and wavelength dispersive X-ray spectroscopy (WDS) techniques were used to investigate the microstructure and chemical composition of the coatings. The arc sprayed coatings are composed of a lamellar microstructure with low porosities, unmelted particles, and high oxides at the intersplats. A uniform and compact coating with minimal oxides and porosity was achieved for all coatings via HVOF technique. In single-layer coatings, arc spray coating surpasses HVOF coating owing to its oxide layers, which impede sulfuric solution penetration and bolster resistance against electrolyte infiltration. Double-layer coatings, comprising a bonding layer and a top coating, using the same thermal spray method have shown to enhance corrosion resistance.

New quaternary eutectic Al-Cu-Ca-Si system for designing precipitation hardening alloys

The aluminum corner of the previously unexplored quaternary eutectic Al-Cu-Ca-Si system promising for the design of new heat treatable alloys have been studied using thermodynamic modeling and experimental techniques. The experimental data have revealed the presence in equilibrium of a previously undescribed quaternary compound identified as a strict stoichiometric Al2CaSiCu phase with a tetragonal I4/mmm structure (Pearson symbol: tI10) and the lattice parameters a = 4.04 Å and c = 11.00 Å. The phase has a density of 3.36 g/cm3 and a microhardness of 335 Hv. In accordance with the suggested structure of the phase diagram, its region that can be promising for the design of heat treatable alloys contains three (Al)+Al2Cu+Al2CaSiCu, (Al)+Al2Si2Ca+Al2CaSiCu and (Al)+Al2Cu+Al2Si2Ca quasi-ternary sections and two (Al)+Al2Cu+Al2Si2Ca+Al2CaSiCu and (Al)+Al2Cu+Al2CaSiCu+Si four-phase fields. Analysis of the precipitation hardening response for the new quaternary Al-5 wt%Cu-Ca-Si alloys suggests that it is not inferior (the obtained peak hardness is ∼125 Hv) to that for the alloys Al-5 wt% Cu (∼120 Hv) and Al-4 wt%Si-5 wt%Cu (∼125 Hv) based on the conventionally used systems. However, to obtain noticeable hardening at aging, the content of silicon should be at least 1.1–1.2 times higher than that of calcium. A comparative hot tearing susceptibility (HTS) study revealed that the new heat treatable Al-5 wt%Cu-Ca-Si alloys have higher hot tearing resistances (HTS ∼16 mm according to a pencil probe) than that of the Al-5 wt%Cu base alloy (HTS >16 mm).