Effects of Si and Cu contents on grain size of Al–Si–Cu alloys

The influence of the silicon and copper contents on the grain size of high-purity Al–Si, Al–Cu, and Al–Si–Cu alloys was investigated. In the Al–Si alloys, a poisoning effect was observed and a poor correlation between the grain size and growth restriction factor was obtained. A possible cause of the poisoning effect in these alloys is the formation of a TiSi₂ monolayer on the particles acting as nucleation sites or another poisoning mechanism not associated with TiSi₂ phase formation. In the Al–Cu alloys, a good correlation between the grain size and growth restriction factor was found, whereas in the Al–Si–Cu alloys, the correlation between these two parameters was inferior.     

The electrochemical properties of melt-spun Al–Si–Cu alloys

Melt spinning was used to prepare Al_75−XSi₂₅Cu_X (X = 1, 4, 7, 10 mol%) alloy anode materials for lithium-ion batteries. A metastable supersaturated solid solution of Si and Cu in fcc-Al, α-Si and Al₂Cu co-existed in the alloys. Nano-scaled α-Al grains, as the matrix, formed in the as-quenched ribbons. The Al₇₄Si₂₅Cu₁ and Al₇₁Si₂₅Cu₄ anodes exhibited initial discharge specific capacities of 1539 mAh g⁻¹, 1324 mAh g⁻¹ and reversible capacities above 472 mAh g⁻¹, 508 mAh g⁻¹ at the 20th cycle, respectively. The specific capacities reduced as the increase of the Cu content. AlLi intermetallic compound was detected in the lithiated alloys. It is concluded that the lithiation mechanism of the Al–Si-based alloys can be affected by the third component. The structural evolution and volume variation can be mitigated due to the formation of non-equilibrium state and the co-existence of nano-scaled α-Al, α-Si, and Al₂Cu for the present alloys.     

Growth direction and Si alloying affecting directionally solidified structures of Al–Cu–Si alloys

The roles of growth direction and Si content on the columnar/equiaxed transition and on dendritic spacings of Al–Cu–Si alloys still remain as an open field to be studied. In the present investigation, Al–6 wt-%Cu–4 wt-%Si and Al–6 wt-%Cu alloys were directionally solidified upwards and horizontally under transient heat flow conditions. The experimental results include tip growth rate and cooling rates, optical microscopy, scanning electron microscopy energy dispersive spectrometry and dendrite arm spacings. It was found that silicon alloying contributes to significant refinement of primary/secondary dendritic spacings for the upward configuration as compared with corresponding results of the horizontal growth. Experimental growth laws are proposed, and the effects of the presence/absence of solutal convection in both growth directions are discussed.     

Decomposition of supersaturated solid solutions in Al–Cu–Mg–Si alloys

The Al–Cu–Mg–Si alloying system is a base for a diverse group of commercial alloys which acquire their properties after quenching and aging. Therefore, the knowledge of the phase composition of hardening precipitates and the conditions under which they are formed is very important. ast reference data were analyzed along with experimental results and calculations of phase equilibria. Different alloys were compared based on the composition of the supersaturated solid solution. It is shown that the phase composition of aging products in alloys with Mg : Si > 1 agrees well with the equilibrium phase composition at a temperature of annealing. However, the sequence of precipitation in the alloys with Mg : Si < 1 is more complicated. The hardening in these alloys occurs with precipitation of the and phases and their precursors. The former phase may contain copper and later transforms either to and (Mg₂Si) or to Q phase depending on the amount of copper and annealing temperature.     

Liquid–Liquid Interfacial Tension in Ternary Monotectic Alloys Al–Bi–Cu and Al–Bi–Si

The liquid–liquid interfacial tension in the ternary monotectic alloys Al_34.5-x Bi_65.5Cu _x and (Al_0.345Bi_0.655)_100-x Si _x (mass%) has been determined as a function of its Cu (Si) content by a tensiometric technique. It is established that the interfacial tension gradually increases when either Cu or Si is added to Al–Bi alloys. The increase of can be related to the increase of the miscibility gap (both width and height) when Cu (Si) is added to the Al–Bi binary. The temperature dependences of the interfacial tension in binary Al_34.5Bi_65.5 and ternary Al_23.25Bi_65.5Cu_11.25 and (Al_0.345Bi_0.655)₉₅Si₅ monotectic alloys are well described by the power function with the critical-point exponent .     

The fatigue damage development in a cast Al–Si–Cu alloy

The experimental identification of fatigue damage mechanisms and evaluation of their development rate, based on changes in material respond on cycle loading, has been presented in the work. The research has been conducted on hyper-eutectic cast alloy AlSi8Cu3. The microstructure and fracture analyses were performed. The high cycle fatigue tests were conducted with frequency of 20 Hz under constant nominal stress amplitude with monitoring the strain response of material during the test. The ratcheting was found as the main mechanism of the fatigue damage. It was established that the linear fatigue accumulation law should not be used for fatigue life prediction in case of the tested cast aluminum alloy.     

Incipient melting of Al5Mg8Si6Cu2 and Al2Cu intermetallics in unmodified and strontium-modified Al–Si–Cu–Mg (319) alloys during solution heat treatment

The present work was performed on seven alloys containing in common Al–6.5 wt%Si–3.5 wt%Cu, with magnesium in the range 0.04–0.45 wt%, and strontium in the range 0–300 p.p.m. The alloys were cast in the form of tensile test bars, solution heat treated in the temperature range 480–540°C for times up to 24 h. Two types of solution heat treatment were applied: (i) single-stage, where the test bars were solution treated at a certain temperature for 12 h prior to quenching in hot water (60°C); (ii) two-stage, where the test bars were solution treated for 12 h/510°C+12 h/T°C (T=510, 520, 530, 540°C), followed by quenching in hot water. In the low-magnesium alloys (i.e. with Mg0.04 wt%), melting of the Al2Cu phase commenced at 540°C. Increasing the magnesium content to 0.5 wt% reduced the incipient melting temperature of the Al5Mg8Si6Cu2 phase to 505°C. The mechanism of incipient melting and its effect on the tensile properties have been discussed in detail. © 1998 Chapman & Hall     

High strength Al–Zn–Mg–Cu–Ni–Si alloy with improved casting properties

Abstract

The casting properties of high strength Al-7Zn-7Mg-1Cu-3Ni-3Si(wt-%) alloy are described. Compared with common Al-Zn-Mg-Cu alloys, an improvement of casting properties has been achieved by adding elements (Ni, Mg, Si) that form eutectic phases, thus reducing the solidification interval of the alloy. A comparison of thermal cooling curves, castability and hot tearing tendency has been carried out for three alloys: Al-7Zn-2Mg-1Cu (structure consists mainly of solid solution), quasi-ternary eutectic alloy Al-7Zn-7Mg-1Cu-3Ni-3Si and the common casting alloy Al-10Si. In addition, the effect of melt protection against oxidation on castability has been evaluated. It is shown that the casting properties of the protected quasi-ternary eutectic alloy are significantly better than those of the common Al-7Zn-2Mg-1Cu alloy and that they achieve a level close to that of Al-10Si alloy.     

Phase stabilization principle and precipitate-host lattice influences for Al–Mg–Si–Cu alloy precipitates

In this work, we seek to elucidate a common stabilization principle for the metastable and equilibrium phases of the Al–Mg–Si–Cu alloy system, through combined experimental and theoretical studies. We examine the structurally known well-ordered Al–Mg–Si–Cu alloy metastable precipitates along with experimentally observed disordered phases, using high angle annular dark field scanning transmission electron microscopy. A small set of local geometries is found to fully explain all structures. Density functional theory based calculations have been carried out on a larger set of structures, all fully constructed by the same local geometries. The results reveal that experimentally reported and hypothetical Cu-free phases from the set are practically indistinguishable with regard to formation enthalpy and composition. This strongly supports a connection of the geometries with a bulk phase stabilization principle. We relate our findings to the Si network substructure commonly observed in all Mg–Al–Si(–Cu) metastable precipitates, showing how this structure can be regarded as a direct consequence of the local geometries. Further, our proposed phase stabilization principle clearly rests on the importance of metal-Si interactions. Close links to the Al–Mg–Si precipitation sequence are proposed.     

Metallurgical parameters controlling the microstructure and hardness of Al–Si–Cu–Mg base alloys

Castings were prepared from both experimental and industrial 319 alloy melts containing 0–0.6 wt% Mg. Test bars were cast in two different cooling rate molds, a star-like permanent mold and an L-shaped permanent mold, with DASs of 24 μm and 50 μm, respectively. The bars were tempered at 180 °C (T6 treatment) and 220 °C (T7 treatment) for 2–48 h. The results showed that Mg content, aging conditions, and cooling rate have a significant effect on the microstructure of both experimental and industrial alloys and, consequently, on the hardness. The addition of Mg resulted in the precipitation of the β-Mg₂Si, Q-Al₅Mg₈Cu₂Si₆, π-Al₈Mg₃FeSi₆ and of the block-like θ-Al₂Cu phases. The Mg and Cu, as well as the higher cooling rates improved the hardness values, especially in the T6 heat-treated condition, whereas the addition of Sr decreased these values.     

Effect of Zn addition on two-step aging behaviour of Al–Mg–Si–Cu alloy

This study investigates the effect of Zn addition two-step behaviour in an Al–Mg–Si–Cu alloy. During pre-aging at 100°C for 3?h, the Zn can partition into clusters because of the strong Zn–Mg interaction, prompting the formation of clusters. During subsequent artificial aging at 180°C for up to 240?min (peak hardness condition), the Zn does not significantly partition into clusters or precipitates, and the majority of Zn remains in the Al matrix. However, the presence of Zn in the matrix stimulates the transformation from clusters to GP zones to β′′ phases. The enhanced formation of GP zones and β′′ phases correlates well with the remarkable age-hardening response.     

Microstructure and Mechanical Properties of Rapidly Solidified Hypereutectic Al–Si and Al–Si–Fe Alloys

The microstructure and mechanical properties of rapidly solidified Al–18 wt% Si and Al–18 wt% Si–5 wt% Fe alloys were investigated by a combination of optical microscopy, scanning electron microscopy, transmission electron microscopy, x-ray diffraction, tensile testing, and wear testing. The centrifugally atomized binary alloy powder consisted of the -Al (slightly supersaturated with Si) and Si phases and the ternary alloy powder consisted of the -Al (slightly supersaturated with Si), silicon, and needle-like metastable Al–Fe–Si intermetallic phases. During extrusion the metastable -Al₄FeSi₂ phase in the as-solidified ternary alloy transformed to the equilibrium -Al₅FeSi phase. The tensile strength of both the binary and the ternary alloys decreased with a high-temperature exposure, but a significant fraction of the strength was retained up to 573 K. The specific wear gradually increased with increasing sliding speed but decreased with the addition of 5 wt% Fe to the Al–18 wt% Si alloy. The wear resistance improved with annealing due to coarsening of the silicon particles.     

Effects of Al–8.5Si–25Cu–xY filler metal foils on vacuum brazing of SiCp/Al composites

Rapidly solidified Al–8.5Si–25Cu–xY (wt-%, x?=?0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5) foils were used as filler metal to braze Al matrix composites with high SiC particle content (SiCp/Al-MMCs), and the filler presented fine microstructure and good wettability on the composites. The joint shear strength first increased, then decreased and a sound joint with a maximum shear strength of 135.32?MPa was achieved using Al–8.5Si–25Cu–0.3Y as the filler metal. After Y exceeded 0.3%, a needle-like intermetallic compound, Al3Y, was found in the brazing seam, resulting in a dramatic decline in the shear strength of the brazed joints. In this research, the Al–8.5Si–25Cu–0.3Y filler metal foil was found to be suitable for the brazing of SiCp/Al-MMCs with high SiC particle content.     

Eutectic Al–Si–Cu–Fe–Mn alloys with enhanced mechanical properties at room and elevated temperature

In this paper, we report a novel kind of eutectic Al–Si–Cu–Fe–Mn alloy with ultimate tensile strength up to 336 MPa and 144.3 MPa at room temperature and 300 °C, respectively. This kind of alloy was prepared by metal mold casting followed by T6 treatment. The microstructure is composed of eutectic and primary Si, α-Fe, Al₂Cu and α-Al phases. Iron-rich phases, which were identified as BCC type of α-Fe (Al₁₅(Fe,Mn)₃Si₂), exist in blocky and dendrite forms. Tiny blocky Al₂Cu crystals disperse in α-Fe dendrites or at the grain boundaries of α-Al. During T6 treatment, Cu atoms aggregate from the super-saturation solid solution to form GP zones, θ″ or θ′. Further analysis found that the enhanced mechanical properties of the experimental alloy are mainly attributed to the formation of α-Fe and copper-rich phases.     

Microstructure and mechanical properties of Al–Si–Mg–Cu–Ti alloy with trace amounts of scandium

The effect of Sc on the microstructure and mechanical properties of Al–Si–Mg–Cu–Ti alloy was investigated. Results obtained in this research indicate that, with increasing Sc content, the microstructure of the investigated alloys exhibits finer equiaxed dendrites with rounded edges and the morphology of the eutectic Si shows a complete transition from a coarse needle-like structure to a fine fibrous structure upon modification of eutectic Si. Subsequent T6 heat treatment had further induced the precipitation of nano-scaled secondary Al₃(Sc, Ti) phase, as well as spheroidisation of eutectic Si. Combined with T6 heat treatment, the ultimate tensile strength, yield strength, percentage elongation and hardness were achieved in 0.20?wt-% Sc-modified alloy.     

The segregation of copper and silicon in Al–Si–Cu alloy during electromagnetic centrifugal solidification

The present paper investigates the segregation of copper and silicon in an Al–1wt%Cu–1wt%Si alloy solidified under the co-action of centrifugal and electromagnetic forces. The reasons for the solute segregation and the effect of electromagnetic force on segregation are discussed. Tubular samples cut from the solidified alloy are analyzed, the results showing that the segregation of copper and silicon occurs along the normal direction of the samples and that the electromagnetic field has a remarkable influence on the segregation of both copper and silicon. As the exciting current increases, the segregation of copper decreases, while the segregation of silicon first increases and then decreases. The migration of solute atoms in the melt depends not only on the density difference between the solute and aluminum atoms, but also on the strength of the electromagnetic force. The magnetic force changes the rotation velocity of the melt, reduces the migration velocity of copper and causes the reduction of copper segregation. Because of the difference of the electrical conductivity between the solute and the aluminum melt, the reductions of velocity are not equal.     

High-temperature deformation behavior of Cu–6.0Ni–1.0Si–0.5Al–0.15?Mg–0.1Cr alloy

The hot compression deformation behavior of Cu–6.0Ni–1.0Si–0.5Al–0.15?Mg–0.1Cr alloy with high strength, high stress relaxation resistance and good electrical conductivity was investigated using a Gleeble1500 thermal–mechanical simulator at temperatures ranging from 700 to 900?°C and strain rates ranging from 0.001?to 1?s^?1. Working hardening, dynamic recovery and dynamic recrystallization play important roles to affect the plastic deformation behavior of the alloy. According to the stress–strain data, constitutive equation has been carried out and the hot compression deformation activation energy is 854.73?kJ/mol. Hot processing map was established on the basis of dynamic material model theories, and Prasad instability criterion indicates that the appropriate hot processing temperature range and strain rate range for hot deformation were 850~875?°C and 0.001~0.01?s^?1, which agreed well with the hot rolling experimentation results.     

High- and low-cycle fatigue influence of silicon,copper, strontium and iron on hypo-eutectic Al–Si–Cu and Al–Si–Mg cast alloys used in cylinder heads

In this publication, ambient condition fatigue investigations with different types of Al–Si–Cu and Al–Si–Mg cast alloys in rotating-bending high-cycle fatigue (HCF) and push–pull low-cycle fatigue (LCF) regimes have been performed with varying Si, Cu, Fe and Sr contents. The cast alloys investigated here are common used in cylinder heads for automotive application. Because the cylinder head is one of the most fatigued parts in combustion chamber engines, the microstructural knowledge of the damage process provides a tool of construction and its material selection. The investigations were also supported with an in-situ microstructural crack observation in high plasticity rotating-bending regimes. The specimens were directly processed out of serial produced T79 heat-treated cylinder heads to provide the equal microstructure for testing as under operational conditions.The observations clearly identified the effects of the individual alloying elements both under low- and high-cycle fatigue. The crack propagation speed and the crack paths were majorly influenced by the eutectic silicon. Additional, the precipitation hardening due to copper affected significantly the fatigue endurance, too. In high plasticities the silicon’s influence got almost lost and only the matrix strength was crucial. Thus, increased fatigue strength in high loaded LCF regimes was observed for alloys with less copper content, thus higher ductility. By contrast, improved HCF and low loaded LCF endurance was only achieved when the matrix strength was increased by copper’s precipitation hardening. Crack branching and deflections strongly influenced the microstructural damage of the ductile AlSi7Mg(Sr) and hence, gained its fatigue strength. Iron phases could not identified as harmful inclusions, since the phases were similar in size of other hard phase elements like the other primary intermetallic phases like ${\text{Al}}_2\text{Cu}$ and β-$\text{Si}$ phases under notch stress aspects, by the well defined solidification process in the test section. Because the crack nucleation mainly occurred on Si particles, strontium as a refinement agent influenced the early crack onset and accordingly the fatigue in total. Thus, the AlSi6Cu4(Sr) had increased lifetimes compared to AlSi6Cu4 both in HCF and LCF. Further, the presented results provide a modification of the Manson–Coffin approach to describe the relationship between plastic strain and lifetime, valid for all proposed alloys with only one set of parameters. Thus, it was possible to perform the fatigue calculation with a reduced range of scatter.     

Effects of Cu content on microstructure and mechanical properties of Al–14.5Si–0.5Mg alloy

This study elucidates how Cu content affects the microstructure and mechanical properties of Al–14.5Si–0.5Mg alloy, by adding 4.65 wt.% and 0.52 wt.% Cu. Different Fe-bearing phases were found in the two alloys. The acicular β-Al₅FeSi was found only in the high-Cu alloy. In the low-Cu alloy, Al₈Mg₃FeSi₆ was the Fe-bearing phase. Tensile testing indicated that the low-Cu alloy containing Al₈Mg₃FeSi₆ had higher UTS and elongation than the high-Cu alloy containing the acicular β-Al₅FeSi. It is believed that the presence of the acicular β-Al₅FeSi in the high-Cu alloy increased the number of crack initiators and brittleness of the alloy. Increasing Cu content in the Al–14.5Si–0.5Mg alloy also promoted solution hardening and precipitation hardening under as-quenched and aging conditions, respectively. The hardness of the high-Cu alloy therefore exceeded that of low-Cu alloy.     

Microstructure and brazeability of SiC nanoparticles reinforced Al–9Si–20Cu produced by induction melting

The effect of 0.5?wt-% SiC nanoparticle addition on microstructure and brazeability of Al–9Si–20Cu alloys has been investigated. The brazing is performed using the filler at 550°C for 30?min. Microstructural observations reveal the refinement of Si and CuAl₂ in Al–9Si–20Cu–0.5SiC composite. The average size of Si particles decreases from ～9 to ～4?μm. It has been shown that SiC nanoparticles improve the filler brazeability; the spreading ratio increases up to 88.4% as compared to 76.67% over Al–9Si–20Cu alloy. The tensile strength and ductility of Al–9Si–20Cu–0.5SiC are also enhanced by 47 and 53% respectively. The melting point shows a depression ～4°C in Al–9Si–20Cu–0.5SiC and thus can be a potential filler candidate for brazing industries.