Effect of heat treatment and Fe content on the microstructure and mechanical properties of die-cast Al–Si–Cu alloys

The effect of solution and ageing heat treatment on the microstructure and mechanical properties of the die-cast Al–9 wt.%Si–3.5 wt.%Cu alloys containing 0.1–1.0 wt.% Fe was investigated. The results showed that the dendritic primary α-Al phase was varied from 20 to 100 μm in size and the globular α-Al grains were smaller than 10 μm in size. The Fe-rich intermetallics exhibited coarse compact or star-like shapes with the sizes from 10 to 20 μm and the fine compact particles at an average size of 0.75 μm. The solution treatment of the alloys could be achieved in a short period of time, typically 30 min at 510 °C, which dissolved the Cu-rich intermetallics into the primary α-Al phase and spheroidised the eutectic Si phase. During the subsequent ageing treatment, numerous fine precipitates of θ′ and Q′ phases were formed to provide effective strengthening to the α-Al phase, significantly improving the mechanical properties. Therefore, Fe content in the die-cast Al–Si–Cu alloys needs to be controlled at a low level in order to obtain the improved ductility and strength under solution and aged condition.     

Effect of rolling conditions on the structure and shape memory properties of Fe–Mn–Si alloys

Lattice defects play an important role in controlling the γ → ε martensitic transformation in shape memory ferrous alloys. This work focuses on the relation between various rolling and annealing processes, the microstructure resulting from the processes, and strain recovery of two Fe–Mn–Si alloys with different stacking fault energies (SFEs). Rolling experiments, conducted over a temperature range from 20 °C to 1000 °C, produce quite different microstructures, which vary from a high dislocation density to a structure containing only few isolated dislocations. In addition, annealing temperature has a very important influence not only on the dislocation arrays but also on the stacking faults remaining in the austenite, whose density depends on the SFE value for the alloy. Within the framework of the processing parameters selected for this work, i.e. roll speed, rolling reductions, processing temperatures and schedules, rolling at intermediate temperatures and annealing at a temperature of 650 °C seem to be the most appropriate methods to obtain a microstructure favorable for a nearly full degree of shape recovery.     

Fe–Al–Mn–C lightweight structural alloys: a review on the microstructures and mechanical properties

Abstract

Adding a large amount of light elements such as aluminum to steels is not a new concept recalling that several Fe–Al–Mn–C alloys were patented in 1950s for replacement of nickel or chromium in corrosion resistance steels. However, the so-called lightweight steels or low-density steels were revisited recently, which is driven by demands from the industry where steel has served as a major structural material. Strengthening without loss of ductility has been a triumph in steel research, but lowering the density of steel by mixing with light elements will be another prospect that may support the competitiveness against emerging alternatives such as magnesium alloys. In this paper, we review recent studies on lightweight steels, emphasizing the concept of alloy design for microstructures and mechanical properties. The influence of alloying elements on the phase constituents, mechanical properties and the change of density is critically reviewed. Deformation mechanisms of various lightweight steels are discussed as well. This paper provides a reason why the success of lightweight steels is strongly dependent on scientific achievements even though alloy development is closely related to industrial applications. Finally, we summarize some of the main directions for future investigations necessary for vitalizing this field of interest.     

Effect of silicon content on the microstructure and properties of Fe–Cr–C hardfacing alloys

In this study, the surface of St52 steel was alloyed with preplaced powders 55Fe39Cr6C, 49Fe39Cr6C6Si, and 45Fe39Cr6C10Si using a tungsten-inert gas as the heat source. Following surface alloying, conventional characterization techniques, such as optical microscopy, scanning electron microscopy, and X-ray diffraction were employed to study the microstructure of the alloyed surface. Microhardness measurements were performed across the alloyed zone. Room-temperature dry sliding wear tests were used to compare the coatings in terms of their tribological behavior. It was found that the as-deposited coatings contained higher volume fractions of carbides (Cr₇C₃). The presence of 6%Si in the preplaced powders caused an increase in microhardness and wear resistance.     

Damping behaviour and mechanical properties of rapidly solidified Al–Fe–Mo–Si/Al alloys

In order to develop a new high damping aluminium alloy with strength and toughness for advanced aircraft structure application, rapidly solidified (RS) Al–Fe–Mo–Si/Al alloys were synthesized. The damping behaviour, mechanical properties and microstructures of the alloys were studied. Results showed that the damping capacities of RS Al–Fe–Mo–Si/10–15% Al alloys are stable between 7.0–10.0×10-3 at room temperature, which almost reach the high damping threshold, 10.0×10-3. At lower frequency (0.1–10 Hz) the damping capacity is decidely frequency and temperture dependent above 50°C, with lowest frequency and highest temperature resulting in the highest less factor. It was noted that mechanical properties of the Al–Fe–Mo–Si/10–15% Al alloys are both excellent at room temperature (b=536–564 MPa, =7.2–11.4%) and at elevated temperature (250°C: b=295–324 MPa). Analysis of microstructures reveal that the damping capacity arises from deformation of the pure Al areas, and strength at elevated temperature from the dispersion strengthening of intermetallic phase. © 1998 Chapman & Hall     

Effect of aluminium on the microstructure and mechanical properties of as-cast magnesium–manganese alloys

In this paper, the effect of aluminium on microstructure and mechanical properties of as-cast magnesium–manganese alloy has been investigated by means of X-ray diffraction, optical microscopy and scanning electron microscopy. The results reveal that various Al–Mn intermetallic compounds form with an increase of Al content. As a result, microstructure of AM11 alloy has been effectively refined due to the formation of Al₈Mn₅ phase along the grain boundary, while Al addition is explained as the main reason on refining the microstructure of AM91 alloy due to its higher grain growth restriction factor value of ～4.32. The tensile yield strength (TYS) has been improved steadily from 27.4 to 122.9?MPa with increasing Al content, because of the combined effects of grain boundary strengthening, solid solution strengthening and precipitation hardening behaviours.     

The effects of cell spacing and distribution of intermetallic fibers on the mechanical properties of hypoeutectic Al–Fe alloys

The aim of the present investigation was to contribute to provide a basis for understanding how to control solidification parameters, microstructure and mechanical strength of Al–Fe alloys. Upward directional solidification experiments have been carried-out with commercially pure Al and Al–0.5 wt.% Fe, Al–1.0 wt.% Fe and Al–1.5 wt.% Fe alloys. The tensile tests results have been correlated to cell spacing (λ₁), since cellular growth has prevailed along all obtained Al–Fe castings. The used casting assembly was designed in such way that the heat was extracted only through the water-cooled system at the bottom of the casting. In order to investigate the nature of Al–Fe intermetallic fibers, they were extracted from the aluminum-rich matrix by using a dissolution technique. These fibers were then investigated by SEM-EDAX microscopy. It was found that the ultimate tensile strength, yield tensile strength and elongation increase with decreasing cell spacing. The highest ultimate tensile strength was that obtained for the most refined microstructure, i.e. for the Al–1.5 wt.% Fe alloy sample, where a higher density of eutectic fibers was found distributed in a more homogeneous way along the casting section due to lower cell spacings. In contrast, the elongation was found to decrease with increasing solute content.     

Effect of CeLa addition on the mechanical properties of Al–Cu–Mn–Mg–Fe alloy

The rapid development of new energy automobiles leads to an increasing demand for high-strength lithium battery shell alloy. The microstructures, electrical conductivity and mechanical properties of CeLa-containing Al–Cu–Mn–Mg–Fe alloys were investigated with scanning electron microscopy (SEM), X-ray diffraction, Eddy Current conductivity tester, tensile testing and Erichsen cup testing. Experiment results indicate that Al₆(Mn, Fe) particles could be refined by CeLa alloying and AlCuCeLa phase nucleates and grew up at the surface of Al₆(Mn, Fe) particle. Major texture of the CeLa-containing alloys was different from that of the CeLa-free alloy. The electrical conductivity decreased with increase of the CeLa content. CeLa addition could greatly enhance the tensile strength of the alloy at temperatures ranging from –40°C to 300°C.     

Effect of Al addition on the grain refinement and mechanical properties of as-cast Mg–5Y–4Sm alloys

Journal of Materials Science - In recent years, the utilization of Al as a grain refiner in Mg–RE alloys has gained widespread attention because of its advantages such as low cost. In this...     

Effect of ultrasonic treatment on the mechanical behaviour of Al–Ni alloys

Applications of Al–Ni alloys are limited because their matrix is weaker than other binary aluminium alloys. Ultrasonic treatment (UST) is an effective tool for grain refinement that can strengthen the matrix phase. It not only reduces the grain size and porosity but also refines and uniformly distributes the secondary phase, which can influence the mechanical properties of Al–Ni alloys. Varying the amount of nickel (1, 2, 3, and 5?wt-%) in molten aluminium along with ultrasonication of the melt is investigated through grain-structure, mechanical properties, and fractography. Mechanical properties of the alloys subjected to UST are superior to respective as-cast alloys. UST also altered the fracture behaviour from dominant ductile fracture in as-cast alloys to dominant mixed mode fracture.     

Effect of Al content on stacking fault energy in austenitic Fe–Mn–Al–C alloys

Effect of Al content on the stacking fault energy (SFE) was investigated in the austenitic Fe–25Mn–(1.16–9.77)Al–0.68C (at%) alloys by X-ray diffraction line profile analysis and thermodynamic estimation, and was discussed on the basis of anomaly in shear modulus caused by the antiferromagnetic transition. The experimental results show that the stacking fault probability decreases with increasing Al content, the observed SFE increases linearly when Al content is lower than 6.27 at%, and markedly as it is more than 6.27 at%. The thermodynamic estimation indicates that the non-magnetic component of SFE increases faster than the observed one with increasing Al content in the antiferromagnetic state, and both are almost equal in the paramagnetic state. The magnetic order increases SFE in the antiferromagnetic state, and the magnetic component of SFE depends on the average magnetic moment and Néel temperature. The increases in the localized magnetic moment and the decrease in the Néel temperature are caused by the addition of Al atoms into the austenitic Fe–Mn alloys and are accompanied by the anomaly in shear modulus, which affects SFE in the antiferromagnetic state. The anomalous drop in shear modulus leads to the inconsistency for the variations of the observed SFE and non-magnetic component with Al content in the antiferromagnetic state.     

Effect of Cu/Zn on microstructure and mechanical properties of extruded Mg–Sn alloys

In this paper, the effect of Cu and Zn addition on mechanical properties of indirectly extruded Mg–2Sn alloy was investigated. Mg–2Sn–0.5Cu alloy exhibits a moderate yield strength (YS) of 225?MPa and an ultimate strength of 260?MPa, which are much higher than those of the binary Mg–2Sn alloy, and the elongation (EL) evolves as ～15.5%. Mechanical properties of the Mg–2Sn–0.5Cu alloy are deteriorated with more 3 wt-% Zn addition, and YS and EL are reduced as 160?MPa and ～10%. The detailed mechanism is discussed according to the work-hardening rate and strengthening effect related to the grain sizes, second phases and macro-textures. Grain refinement and proper texture are believed to play a critical role in both strength and ductility optimisation.     

Precipitation of iron-rich intermetallics and mechanical properties of Al–Si–Mg–Fe alloys with Al–5Ti–B

Effects of added Al–5Ti–B master alloys on precipitation of iron-rich intermetallics and mechanical properties of A356 cast alloys with high Fe content (1.5?wt-%) were investigated using image analysis, scanning electron microscopy, and tensile testing. Results show that added Al–5Ti–B has apparent refinement on α (Al) grain size of A356 alloys that have high Fe content. 12?wt-% Al–5Ti–B is beneficial for improving mechanical properties of A356 cast alloys with high Fe content. Improved mechanical properties can be attributed to refined microstructure, the proper amounts of TiB₂ and Ti(AlSi)₃, and decreased porosity. An excessive amount of Al–5Ti–B deteriorates mechanical properties of alloys because it leads to the formation of large secondary intermetallics and increased porosity.     

Microstructure development and mechanical properties of rapidly solidified Ti–Fe and Ti–Fe–Bi alloys

Even though rapidly solidified Ti–Fe eutectic alloys may achieve good mechanical strength, increase in ductility is already a task to be accomplished. Addition of tin and arrangements of nano- and ultrafine-grain metallic materials have been shown as potential alternatives to overcome such drawback. Also, to address this problem, it seems that alternative alloy chemistries and processing routes must be adopted when manufacturing Ti-based alloys. In the present investigation, Ti–26 wt.%Fe (Ti–24.5 at.%Fe) and Ti–20 wt.%Fe–3 wt.%Bi (Ti–18 at.%Fe–0.7 at.%Bi) alloys have been prepared in a stepped copper mold using centrifugal casting. The as-cast Ti–Fe(–Bi) microstructures were formed by equiaxial arrangements of cells. Finer cell spacing (λ_c) was associated with the Ti–20 wt.%Fe–3 wt.%Bi alloy. The results include cell spacing measurements, segregation profile by X-ray fluorescence (XRF), uniaxial compression tests, optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A wide variation on the scale of the microstructure was noted especially in the case of the Ti–26 wt.%Fe alloy with the λ_c varying from 11−30 μm. This is due to the different cooling conditions of each diameter along the as-cast rod. Hall–Petch type equations are proposed relating σ_max to λ_c. Bi was dissolved in the β-Ti solid solution as well as TiFe compound formed in the cellular structure of the Ti–20 wt.%Fe–3 wt.%Bi.     

Investigation of corrosion and mechanical properties of Al–Cu–SiC–xNi composite alloys

In this study, dry sliding wear behavior and corrosion resistance of Al–Cu–SiC–xNi (x: 0, 0.5, 1, 1.5 wt.%) composites were investigated. Effect of nickel content on the microstructure and hardness of the alloys was also studied. Wear tests were conducted using a ball on disc wear test device. Corrosion behavior of Al–Cu–SiC–xNi composite alloys in 3.5% NaCl solution was investigated by using potentiodynamic polarization, impedance spectroscopy and cronoamperometric methods. The results showed that the hardness of the composite alloy increases with increasing nickel content. Maximum wear resistance is reported with the addition of 1 wt.%Ni. It was determined that corrosion resistance of Al–Cu–SiC composite alloys improved with increasing nickel content in the alloy.     

Effect of heat treatment on microstructure and mechanical properties of Cu–6.9Ni–2.97Al–0.99Fe–1.06Mn alloy

ABSTRACT

The effect of heat treatment on the mechanical properties and microstructures of Cu–6.9Ni–2.97Al–0.99Fe–1.06Mn alloys was investigated. The results show that the microstructure of the as-cast alloy mainly consists of an alpha-copper matrix and γ-phase Ni₃Al particles. The microstructure of the alloy after solution treatment at 950°C for 2?h is a single-phase alpha-copper supersaturated solid solution and the second-phase strengthening disappears. After ageing treatment at 550°C for 6?h, the γ-phase particles are fully precipitated, and the mechanical properties of the alloy are significantly improved. The tensile strength is increased from 305 to 588?MPa. Quasi-cleavage fracture with shallow dimples appeared in the Cu–6.9Ni–2.97Al–0.99Fe–1.06Mn alloy aged at 550°C for 6?h.     

Microstructure and mechanical properties of Mg–9Li–3Al–xGd alloys

The influence of gadolinium on the microstructure and mechanical properties of Mg–9Li–3Al alloy was investigated. Results show that the addition of Gd can effectively refine the α-Mg phase and change the morphology of the α-Mg phase. Meanwhile, the Al₃Gd phase is mainly distributed at the boundaries of the α-Mg phase and inside the α-Mg phase. The mechanical property tests reveal that the addition of Gd can effectively improve the mechanical properties of the as cast alloys. When the content of Gd is 2·0%, the tensile strength and yield stress (engineering stress) reach max values of 188 and 174 MPa respectively. When the content of Gd addition is 2·5%, the elongation of the alloy is 15·7%.     

Thermal stability and mechanical properties of nanocrystalline Fe–Ni–Zr alloys prepared by mechanical alloying

The thermal stability of nanostructured Fe_100?x?y Ni _x Zr _y alloys with Zr additions up to 4 at.% was investigated. This expands upon our previous results for Fe–Ni base alloys that were limited to 1 at.% Zr addition. Emphasis was placed on understanding the effects of composition and microstructural evolution on grain growth and mechanical properties after annealing at temperatures near and above the bcc-to-fcc transformation. Results reveal that microstructural stability can be lost due to the bcc-to-fcc transformation (occurring at 700 °C) by the sudden appearance of abnormally grown fcc grains. However, it was determined that grain growth can be suppressed kinetically at higher temperatures for high Zr content alloys due to the precipitation of intermetallic compounds. Eventually, at higher temperatures and regardless of composition, the retention of nanocrystallinity was lost, leaving behind fine micron grains filled with nanoscale intermetallic precipitates. Despite the increase in grain size, the in situ formed precipitates were found to induce an Orowan hardening effect rivaling that predicted by Hall–Petch hardening for the smallest grain sizes. The transition from grain size strengthening to precipitation strengthening is reported for these alloys. The large grain size and high precipitation hardening result in a material that exhibits high strength and significant plastic straining capacity.     

Effect of strain rate on microstructures and mechanical properties of Fe–18Cr–8Ni steel

The effect of strain rate on deformation microstructures and mechanical properties of Fe–18Cr–8Ni austenitic stainless steel was investigated at strain rates of from 10^?3 to 100?s^?1. The results indicated that the deformation mechanism of steel changes from transformation induced plasticity (TRIP) to TRIP?+?twinning induced plasticity (TWIP) effect when the strain rate is increased from 10^?3 to 100?s^?1. The yield strength of steel increases gradually with strain rate increased, while the tensile strength and elongation first decreases and then increases slowly. The changes in tensile strength and elongation are due to the change of deformation mechanism with the strain rate increased.