Al-rich Matrix Research Articles

Effect of synthesis pressure on the properties of PcBN composites

Polycrystalline cubic boron nitride (PcBN) composites were synthesized under high-temperature and high-pressure (HPHT) conditions using TiC, Al and Ti as binders. This study explores the influence of varying synthesis pressures on the microstructure, interfacial bonding, densification, and mechanical properties of PcBN composites. The test results indicate that as synthesis pressure increased, the diffusion of Al and Ti elements to the surface of cBN particles was enhanced. This facilitates the migration of Ti atoms through the Al-rich matrix to the surface layer of cBN, thus accelerating the chemical interaction. At the highest pressure of 6 GPa, the hardness, flexural strength and fracture toughness of the samples achieved their maximum values: 3719 Hv, 1090 MPa, and 7.6 MPa.m1/2, respectively. Additionally, the material exhibits excellent cutting properties. Crack bridging, crack deflection, particle pullout and transgranular fracture were observed during the fracture process of the samples. Indicating strong interfacial bonding between cBN and the binder, which contributes to the material's enhanced toughness.

Al Alloy Melting Behavior and Interfacial Reactions with Steel Under Natural Convection.

The Al alloy melting behavior and interfacial reactions during the steelmaking process of high-Al automotive steel were investigated in this study. The total dissolution time of Al bars (20 × 20 × 80 mm) in molten steel was quite short, decreasing from 21.4 s to 10.0 s with an increase in bath temperature from 1580 to 1620 °C. The Al alloy melting process at the molten steel temperature of 1600 °C included the formation of a solidified steel layer, the latter's rapid melting, and Al alloy normal melting, while at 1600 °C, the process included a second increase in the thickness of the solidified layer. Because steel elements such as [Fe], [C], [O], and [N] could diffuse during the whole Al alloy melting process, an Fe (Al)-FeAl-FeAl2-Fe2Al5-Al diffusion layer along the direction of the Al-rich matrix could be found at the Fe-Al interface. Moreover, FexO, Al2O3, and unstable AlN inclusions could be observed in the FeAl layer. This study also investigated how to reduce the number of these easily formed inclusions. Decreasing the pre-heating process time and dissolved oxygen content could be useful in decreasing FexO and Al2O3 inclusion formation. Some small-sized AlN inclusions formed in the center of the Al bars where they could not come into contact with the molten steel directly during the melting process; even for the immersion time of only 1 second, these inclusions were not stable in molten steel at the refining temperature and disappeared during the melting process.

CALPHAD-guided design and experimental study on a novel Al-Ti-Nb alloy

We have used a CALPHAD-guided design methodology to develop a novel lightweight Al-Ti-Nb alloy with nearly 50 vol% of in-situ formed trialuminide reinforcement. After compositional optimization, we selected Al87.5Ti6.25Nb6.25 (at%) as the experimental alloy composition and subjected it to a 24-hour homogenization heat-treatment at 475°C for attainment of equilibrium, guided by DSC and CALPHAD-derived melting point data. Phase and microstructure analysis revealed a microstructure with approximately 50 vol% of a FCC Al-rich matrix and 50 vol% of trialuminide phases for strengthening. The experimental onset melting point of the Al-rich matrix was determined to be 647°C, which significantly surpasses Al-Si based high-temperature alloys (577 ℃), showcasing the potential of this alloy as a high-temperature structural material. Nanoindentation tests demonstrated exceptional mechanical properties. The alloy was found to have a microhardness of 3350 MPa, which not only outperformed 7075 Al alloy, A390 Al-Si alloy, and commercially pure Ti but also exceeds the levels of Ti-6Al-4V alloy at nearly 28% lower density. This study's significance lies in its integration of CALPHAD predictions and meticulous microstructural investigation, offering an effective approach for the design and characterization of novel Al-based alloys.

Growth mechanism of highly twinned Al13Fe4 dendrites obtained from a rapidly solidified Al-5at.% Fe melt

We report the formation of large and highly twinned dendrites of the Al13Fe4 approximant phase embedded in an fcc Al-rich matrix. Using a rapid cooling technique, the approximant appears as a 10-fold dendrite. Within each arm, all grains share a common [010] direction. The grain distributions within the arm are quite complex and a single dendrite arm can contain up to four different orientations. Using several techniques, including Electron Back-Scattered Diffraction (EBSD) and Transmission Electron Microscopy (TEM), it has been possible to identify three types of twins, namely {100}, {001} and {201̄} twins. From these observations and previous reports, we propose a growth mechanism to explain the formation of such specific 10-fold motifs. It corresponds to the heteroepitaxial growth of the Al13Fe4 approximant from a well-facetted decagonal Al–Fe quasicrystalline seed.

Eutectic, precipitation-strengthened alloy via laser fusion of blends of Al-7Ce-10Mg (wt.%), Zr, and Sc powders

Laser powder-bed fusion was used to create an Al-7Ce-10Mg-0.71Zr-0.23Sc (wt.%) alloy, using hypoeutectic Al-7Ce-10Mg (wt.%) pre-alloyed powder blended with either elemental Zr and Sc powders (∼20 µm in size), or pre-alloyed, concentrated Al-10Zr and Al-10Sc (wt.%) powders (comprised of 1-5 µm Al3Zr or Al3Sc particles embedded in a <45 μm Al-rich matrix). The effects of process parameters and powder selection on the homogeneity of the as-fabricated microstructure were investigated via metallography and compared to predictions from a simple numerical model describing the dissolution of Zr powders in the melt pool during printing. Both experiments and model show that decreasing scan speed leads to greater dissolution of Zr and Sc, but remelting has no significant effect. The samples produced with Al-10Zr and Al-10Sc powder additions show greater amounts of Zr and Sc dissolution than those produced with elemental Zr and Sc additions, because of the smaller size (5 µm for prealloyed vs. 20 µm for elemental) and lower melting point (1580 and 1320°C for Al3Zr, Al3Sc vs. 1850 and 1541°C for Zr, Sc) of the dissolving species. The alloys fabricated with prealloyed powders display larger amounts of very fine grains (1-2 µm) nucleated by primary L12 Al3(Zr,Sc) precipitates, and a clear hardening response during aging, consistent with supersaturated Zr and Sc forming a high number density of secondary L12 Al3(Zr,Sc) nanoprecipitates.

Dry Sliding Wear Features of an Al-20Sn-5Zn Alloy Affected by Microstructural Length Scales

Al-Sn-Zn alloys are attractive options for use as wear-resistant materials. While Sn promotes self-lubricating characteristics, Zn strengthens the Al-rich matrix. Conventionally, the manufacturing of these alloys involves casting. However, there is still a paucity of studies that associate the solidification microstructure with the wear resistance of these alloys. Inspired by such considerations, this work aims at investigating the wear behavior of an Al-20Sn-5Zn [wt.%] alloy produced by a directional solidification technique. A set of samples with different microstructure length scales was subjected to ball cratering tests using a normal contact load of 0.25 N and six test times. The results show that the dependence of the wear behavior on the microstructure length scale becomes more expressive for longer sliding distances. It was found that coarser microstructures provide an improved wear resistance. In view of that, a possible spectrum of specific wear rates was determined as a function of the sliding distance, considering different microstructure length scales. Finally, experimental equations are proposed to represent a possible range of wear volume and wear coefficient according to the dendrite arm spacings.

Bearing Aluminum-Based Alloys: Microstructure, Mechanical Characterizations, and Experiment-Based Modeling Approach.

Due to the engine's start/stop system and a sudden increase in speed or load, the development of alloys suitable for engine bearings requires excellent tribological properties and high mechanical properties. Including additional elements in the Al-rich matrix of these anti-friction alloys should strengthen their tribological properties. The novelty of this work is in constructing a suitable artificial neural network (ANN) architecture for highly accurate modeling and prediction of the mechanical properties of the bearing aluminum-based alloys and thus optimizing the chemical composition for high mechanical properties. In addition, the study points out the impact of soft and more solid phases on the mechanical properties of these alloys. For this purpose, a huge number of alloys (198 alloys) with different chemical compositions combined from Sn, Pb, Cu, Mg, Zn, Si, Ni, Bi, Ti, Mn, Fe, and Al) were cast, annealed, and tested for determining their mechanical properties. The annealed sample microstructure analysis revealed the formation of soft structural inclusions (Sn-rich, Sn-Pb, and Pb-Sn phases) and solid phase inclusions (strengthened phase, Al2Cu). The mechanical properties of ultimate tensile strength (σu), Brinell hardness (HB), and elongation to failure (δ) were used as control responses for constructing the ANN network. The constructed network was optimized by attempting different network architecture designs to reach minimal errors. Besides the excellent tribological characteristics of the designed set of alloys, soft inclusions based on Sn and Pb and solid-phase Cu inclusions fulfilled the necessary level of mechanical properties for anti-friction alloys; the maximum mechanical properties reached were: σu = 197 ± 7 MPa, HB = 77 ± 4, and δ = 20.3 ± 1.0%. The optimal ANN architecture with the lowest errors (correlation coefficient (R) = 0.94, root mean square error (RMSE) = 3.5, and average actual relative error (AARE) = 1.0%) had two hidden layers with 20 neurons. The model was validated by additional experiments, and the characteristics of the new alloys were accurately predicted with a low level of errors: R ≥ 0.97, RMSE = 1-2.65, and AARE ˂ 10%.

Thermal cyclic resistance and long term inter-diffusion properties of slurry aluminide coatings modified with Si

High temperature oxidation resistant aluminide coatings fail due to their inability to maintain a protective scale. The corresponding mechanism of protection is based on of forming a thin Al2O3 layer, which depends on the availability of Al at the interface with the intermetallic coating. However, the Al content in the coating’s surface decreases with time at high temperatures due to interdiffusion with the substrate and/or frequent regeneration of the protective Al2O3 scale when it spalls. Si addition is known to enhance the life of Ni aluminide coatings under certain corrosion environments. In an effort to develop a stable, long lasting coating for industrial components exposed to metal dusting, diffusion aluminide coating has been produced by applying Al-Si slurries of various compositions on alloy 601. Aluminide coatings were prepared by applying a water base, Al slurry to which 1, 10 and 20 wt. % of Si were added, followed by a diffusion heat treatment. The microstructures of the coatings were similar, exhibiting an outer layer consisting of an Al-rich β-NiAl matrix, an almost stoichiometric β-NiAl inner layer and an interdiffusion zone between the coating and the alloy. Thermal cyclic tests in air at 1100 °C have demonstrated good adhesion and stability of all coatings. In addition, long term isothermal tests at 850 °C for up to 3 months in air showed high oxidation resistance of the coating but different degree of coating degradation depending on the composition. The coating with the lowest Si addition was the most stable.

Microstructure and Indentation Properties of Single-Roll and Twin-Roll Casting of a Quasicrystal-Forming Al-Mn-Cu-Be Alloy

In this investigation, strips of an experimental Al-Mn-Cu-Be alloy were manufactured by high-speed single-roll and twin-roll casting to stimulate the formation of a quasicrystalline phase during solidification. The strips were characterised by light microscopy, scanning and transmission electron microscopy, microchemical analysis, and X-ray diffraction. Indentation testing was used to determine the mechanical responses of the strips in different areas. A smooth surface was achieved on both sides of the twin-roll-cast strip, while the free surface of the single-roll-cast strip was rough. The microstructures in both strips consisted of an Al-rich solid solution matrix embedding several intermetallic phases Θ-Al2Cu, Be4Al (Mn, Cu), Al15Mn3Be2 and icosahedral quasicrystalline phase (IQC). The microstructure of the single-roll-cast strip was more uniform than that of the twin-roll-cast strip. Coarse Al15Mn3Be2 particles appeared in both alloys, especially at the centre of the twin-roll strip. These coarse particles adversely affected the strength and ductility. Nevertheless, both casting methods provided high-cooling rates, enabling the formation of metastable phases, such as quasicrystals. However, improvements in alloy composition and casting procedure are required to obtain enhanced microstructures and properties.

Ag2Al plates in Al–Ag alloys

Abstract The late stages of precipitation in aluminum-rich Al –Ag alloys with silver contents from 3 at.% to 22 at.% were studied with transmission electron microscopy. Shapes, sizes, and arrangements of plates of the stable hexagonal Ag2Al phase forming on {111} planes of the f.c.c. matrix were analysed. The high-angle annular dark-field contrast in scanning transmission electron microscopy is calibrated. This calibration allows for the quantitative measurement of plate thicknesses from high-angle annular dark-field scanning transmission electron micrographs of Ag2Al plates inclined to the electron beam. Results from these measurements are in good agreement with direct bright-field micrographs of plates viewed edge-on. For samples with silver contents above 12 at.% a parallel lamellar arrangement of fine γ-plates and Al-rich matrix is found after extended heat treatments.

The first report on formation of Al-W-Cu grain boundary phase and its influence on mechanical behavior of 2D-WS2 reinforced Al-4Cu alloy matrix composites

Nanostructured two-dimensional (2D) WS2 reinforced Al-4Cu alloy matrix composites were prepared via spark plasma sintering (SPS) at 550 and 570 °C. The microstructure and interface characteristics of the composites were investigated. In situ formation of Al-W-Cu ternary phase at the grain boundaries of the Al-rich matrix phase was observed on sintering. High-resolution transmission electron microscopy (HRTEM) and scanning TEM (STEM) with quantitative mapping confirmed that the structure of ternary Al-W-Cu (Al12W0.6Cu0.4) belongs to bcc phase (space group: Im3̅ (204), similar to that of binary bcc-Al12W phase. Such bcc intermetallic phase was absent in pure Al-matrix under identical sintering conditions. The ternary intermetallic phase along with the retained 2D-WS2 contributed to about 41% increase in the hardness of the alloy composite. Nanoindentation hardness and Young’s modulus of the Al-W-Cu ternary intermetallic were found to be around 4.6 GPa and 104 GPa, respectively. The formation mechanism of Al-W-Cu intermetallic phase from 2D-WS2 nanosheets and Al-4Cu matrix was elucidated with Calphad (Calculation of Phase Diagrams)-based Gibbs energy analysis.

Microstructure and Properties of a Novel Al-Mg-Si Alloy AA 6086

In this work, we investigated a novel Al-Mg-Si alloy, which was developed from an AA 6082, in order to considerably improve the yield and tensile strengths whilst retain excellent ductility. The new alloy possesses a higher content of Si than specified by AA 6082, and, in addition, it contains copper and zirconium. The alloy was characterized in the as-cast condition, after homogenization, extrusion, and T6 heat treatment using light microscopy, scanning and transmission electron microscopy with energy dispersive spectrometry, X-ray diffraction, differential thermal analysis and tensile testing. After T6 temper, tensile strengths were around 490 MPa with more than 10% elongation at fracture. The microstructure consisted of small-grained Al-rich matrix with α-AlMnSi and Al3Zr dispersoids, and Q′-AlCuMgSi and β-Mg2Si-type precipitates.

Evaluating Microstructure, Wear Resistance and Tensile Properties of Al-Bi(-Cu, -Zn) Alloys for Lightweight Sliding Bearings

One of the most important routes for obtaining Al-Bi-x monotectic alloys is directional solidification. The control of the thermal solidification parameters under transient heat flow conditions can provide an optimized distribution of the Bismuth (Bi) soft minority phase embedded into an Al-rich matrix. In the present contribution, Al-Bi, Al-Bi-Zn, and Al-Bi-Cu alloys were manufactured through this route with their microstructures characterized and dimensioned based on the solidification cooling rates. The main purpose is to evaluate the influence of typical hardening elements in Al alloys (zinc and copper) in the microstructure, tensile properties, and wear of the monotectic Al-Bi alloy. These additions are welcome in the development of light and more resistant alloys due to the growing demands in new sliding bearing designs. It is demonstrated that the addition of 3.0 wt.% Cu promotes microstructural refining, doubles the wear resistance, and triples the tensile strength with some minor decrease in ductility in relation to the binary Al-3.2 wt.% Bi alloy. With the addition of 3.0 wt.% Zn, although there is some microstructural refining, little contribution can be seen in the application properties.

Effects of cooling rate and microstructure scale on wear resistance of unidirectionally solidified Al-3.2wt.%Bi-(1; 3) wt.%Pb alloys

Aluminum alloys with soft elements are quite promising in the automotive industry for manufacturing machine elements subjected to relative motion. The combination of some elements makes it possible to highlight some properties, such as the wear resistance. It is also particularly important to understand the role of the microstructural phases’ representative scale in this property. In this research, the joint influence of Bi and Pb on Al-3.2 wt.%Bi-(1; 3) wt.%Pb alloys is analyzed. The alloys were unidirectionally solidified in a water-cooled experimental device under a wide range of solidification cooling rates. The resulting microstructure is formed by droplets containing both Pb and Bi, disseminated in the Al-rich matrix, whose spacing (λG) and diameter (DG) are shown to vary significantly with the cooling rate. Wear tests carried out on samples with different λG and DG showed that the wear volume (Vd) of those with more refined microstructures was lower. Regarding the alloy’s Pb content, it was shown that the one with higher Pb content (3% Pb) has higher wear resistance (lower Vd) and lower wear coefficients for the examined sliding distances of 207, 415, 622 and 829 m, despite preserving a same alloy hardness of about 25 HV.

Transition from high cooling rate cells to dendrites in directionally solidified Al-Sn-(Pb) alloys

The preprogramming of the solidification cooling rate during casting of some Al-based bearing materials, has been used to achieve microstructural patterns conducive to better wear responses. For Al-Sn castings, improvements in the wear resistance were reported to occur when higher amounts of Sn remained segregated in the spacings of the dendritic Al-rich matrix. In this sense, a cellular microstructure could be more adequate since the segregated Sn would be contained along the cells boundaries and not spread through the interstices of multiple dendritic arms. This study investigates a range of Al-xSn alloys compositions (x = 1, 2.6, 7.5, 9, 10 wt.%) and an Al-(9 wt.%)Sn–(1 wt.%Pb), with a view to determining the ranges of Sn concentrations and solidification cooling rates (T˙) for which high cooling rate cells are stable, as well as the reverse cellular/dendritic transition. For T˙ from 1 to 40 K/s, it is shown that for Al-Sn alloys having Sn< 7.5 wt.% the morphology of the Al-rich matrix is fully cellular and for Sn> 10 wt.% it is completely dendritic. The reverse transition from high cooling rate cells to dendrites is shown to occur for the Al-9 wt.%Sn alloy, with T˙ < 3.3 K/s resulting in a dendritic microstructure and T˙ > 6 K/s in a fully cellular Al-rich matrix. The Al-9 wt.%Sn-1 wt.%Pb ternary alloy casting also exhibits a reverse cellular/dendritic transition, with dendrites occurring also for T˙ < 3.3 K/s and cells for T˙ > 8 K/s.

The effects of Cr addition on microstructure, hardness and tensile properties of as-cast Al–3.8wt.%Cu–(Cr) alloys

An investigation is made on the effects of Cr addition (0.25 and 0.50wt%) on the solidification evolution, microstructure formation, hardness and tensile properties of Al–3.8Cu–(Cr) alloys. Solidification experiments were carried out in a vertical furnace using a metallic mold cooled from the bottom, thus permitting solidified ingots under transient heat flow conditions to be obtained. The solidification system was instrumented with thermocouples at positions along the length of the ingot to permit the solidification cooling rate to be determined from bottom to top of the ingots. The ingots were transversally and longitudinally sectioned to extract specimens for metallographic analyze, hardness and tensile tests. The macrostructures are shown to be entirely columnar along the length of the Al–3.8Cu and Al–3.8Cu–0.25Cr alloys ingots, whereas the Al–3.8Cu–0.50Cr alloy is shown to have a columnar-to-equiaxed transition close to the top. For any alloy ingot examined, the Al-rich matrix is characterized by a cellular morphology for high cooling rates followed by cellular/dendritic transitions with the decrease in cooling rate. The addition of Cr to the Al–3.8Cu alloy promoted the formation of Al23CuFe and Al7CuCrFe phases precipitated in the matrix and eutectic mixture, preventing formation of isolated Al–Fe intermetallic compounds. Hardness and tensile strength increased with increasing alloy Cr content, with highest values of both properties associated with the Al–3.8Cu–0.50Cr alloy ingot. Experimental equations correlating hardness/tensile strength and cellular spacing are proposed. These equations were coupled to the theoretical Hunt–Lu model to estimate hardness and ultimate tensile strength as a function of the cellular spacing.

Influence of Constrained High-Pressure Torsion on Microstructure and Mechanical Properties of an Aluminum-Based Metal Matrix Composite

Multilayered Al-Cu composites were fabricated successfully by constrained high-pressure torsion (HPT) in a Bridgeman anvil type unit under an applied pressure of 6.0 GPa after ten turns. Due to the good strain compatibility of Al and Cu, achieved during HPT, separate discs bonded without pores and cracks. Microstructural characterization of the processed disks showed that the originally flat interface between Al and Cu layers transforms, and some bindings and vortice-like folding are formed in a submicron multilayered structure embedded in an Al-rich matrix in almost all volumes. This led to an exceptional increase of ultimate strength. The tensile tests showed the value of the tensile strength reached 485 MPa at room temperature, which is several times higher than in pure aluminum (80 MPa) and copper (190 MPa) subjected to the same processing. Such an increase in the ultimate strength is associated with hardening due to formation of a multiphase fine-grained structure. This study indicates a high potential for the application of high-pressure torsion in bonding of Al and Cu to produce composites with enhanced mechanical properties.

Length scale of solidification microstructure tailoring corrosion resistance and microhardness in T6 heat treatment of an Al–Cu–Mg alloy

ABSTRACT The combined effects of solidification microstructure refining scale and T6 heat treatment conditions on corrosion behaviour and Vickers microhardness of an Al–3 wt-% Cu–0.5 wt-% Mg alloy were studied. Then, representative samples having quite distinct primary dendritic spacings were solution treated at 495°C for 3 h and artificially aged at 200°C during different times. It was found that the feature of finer solidification microstructure having higher corrosion current density and higher microhardness can be inherited to subsequent T6 heat treatments. In contrast to the as-cast condition, the aging times of 0.5 and 1 h were shown to promote lower corrosion rates without corrosion occurring at the central region of Al-rich matrix. On the other hand, the aging time of 3 h led to a significant decrease in both the corrosion resistance and the microhardness. Finally, a comparative analysis with other works from the literature was also conducted.

The Roles of Mn and Ni Additions to Fe-Contaminated Al in Neutralizing Fe and Stabilizing the Cellular α-Al Microstructure

The development of new Al-based alloys has included the addition of transition alloying elements in order to produce phases that are stable at high temperatures. Elements such as Mn, Cr, and V, can lead to supersaturated solid solutions in Al, and elements with low solubility and formers of eutectic systems (e.g., Ni, Fe, Ce) induce mechanical strengthening by the formation of higher fractions of intermetallics. Since Fe is the major impurity in commercial Al and an undesired element in its recycling, another positive effect of both Ni and Mn addition into Al alloys is related to the neutralization of Fe-compounds, known to be harmful to mechanical properties. Both Mn and Ni fulfill the requirements for high-temperature applications, but there is a lack of studies in the literature reporting the relation between microstructure and mechanical properties of Al–Mn–Ni alloys in the as-cast condition. In the present study, Al–1 wt% Mn–(1 wt% Ni) alloys are prepared using Fe-containing Al, which are subjected to directional solidification experiments with a view to producing castings under quite different solidification cooling rates ($${\dot{{T}}}$$) along their lengths. The effects of $${\dot{{T}}}$$ on the morphology of the Al-rich matrix; its characteristic length scale; and composition of the IMCs formed are analyzed. The Al–1 wt% Ni alloy has an Al-rich matrix characterized by a dendritic morphology. However, it is shown that the addition of 1 wt% Mn induces the Al-rich matrix to assume the cellular morphology for $${\dot{{T}}}$$ > 2.3 °C/s. The stabilization of cells for high cooling rates seems to be related to the crystalline structure of the alloying element. Power function experimental equations relating the cellular spacing (λC) of both Al–1 wt% Mn and Al–1 wt% Mn–1 wt% Ni alloys castings are derived, in which the ternary alloy is shown to have λC values about 30% lower than those of the binary alloy. A Hall–Petch-type equation is proposed relating the Vickers microhardness (HV) to λC for the ternary alloy. Moreover, the additions of Mn and Ni to the Fe-containing Al used in the preparation of the alloys seem to be beneficial in neutralizing Fe by forming the Al9(Mn,Fe)Ni IMC, in which Mn is replaced with Fe.

Measurement and interrelation of length scale of dendritic microstructures, tensile properties, and machinability of Al-9 wt% Si-(1 wt% Bi) alloys

Al-Si alloys are increasingly being employed in the aerospace industry, satellite bearings, and inertial navigation systems. Hypoeutectic compositions are more attractive because of the low material cost and excellent castability. The addition of alloying elements to these alloys is generally used to modify the morphology of Si particles with a view to meeting mechanical strength requirements. Considering manufacturing requirements, to efficiently predict the quality of the machining process, it is essential to analyze the machinability of the material to be used, which depends on several factors, including microstructural features. In the present study, the effects of solidification cooling rate and Bi addition to Al-Si alloys on microstructural features, tensile properties, and rate of heat generation during necking processes are analyzed in samples of directionally solidified Al-9 wt% Si-(1.0 wt% Bi) alloy castings. The microstructure is composed of α-Al dendrites characterized by measured primary, secondary, and tertiary dendritic arm spacings, with a eutectic mixture of α-Al and Si-(Bi) particles. The addition of Bi is shown to attenuate the sharp tips of Si crystals. The dendritic length scale of the Al-rich matrix is correlated with the solidification cooling rate through experimental equations, and the evolution of the ultimate tensile strength with the primary dendritic spacing is experimentally represented by a single Hall-Petch-type equation for both examined alloys. Considering a same primary dendritic arm spacing, the addition of 1 wt% Bi to the Al-9 wt% Si alloy is shown to have the following effects: similar ultimate tensile strength, the elongation to fracture is improved, higher machinability based on significant decrease in the heating rate.