Effect of Cu addition on microstructures and tensile properties of high-pressure die-casting Al-5.5Mg-0.7Mn alloy

In this study, Cu was added into the high-pressure die-casting Al-5.5Mg-0.7Mn (wt%) alloy to improve the tensile properties. The effects of Cu addition on the microstructures, mechanical properties of the Al-5.5Mg-0.7Mn alloys under both as-cast and T5 treatment conditions have been investigated. Additions of 0.5 wt%, 0.8 wt% and 1.5 wt% Cu can lead to the formation of irregular-shaped Al₂CuMg particles distributed along the grain boundaries in the as-cast alloys. Furthermore, the rest of Cu can dissolve into the matrixes. The lath-shaped Al₂CuMg precipitates with a size of 15–20 nm × 2–4 nm were generated in the T5-treated Al-5.5Mg-0.7Mn-xCu (x = 0.5, 0.8, 1.5 wt%) alloys. The room temperature tensile and yield strengths of alloys increase with increasing the content of Cu. Increasing Cu content results in more Al₂CuMg phase formation along the grain boundaries, which causes more cracks during tensile deformation and lower ductility. Al-5.5Mg-0.7Mn-0.8Cu alloy exhibits excellent comprehensive tensile properties under both as-cast and T5-treated conditions. The yield strength of 179 MPa, the ultimate tensile strength of 303 MPa and the elongation of 8.7% were achieved in the as-cast Al-5.5Mg-0.7Mn-0.8Cu alloy, while the yield strength significantly was improved to 198 MPa after T5 treatment.     

Tensile and fatigue properties of Fe-Mn-Al-C alloys

The tensile properties and fatigue behaviour of three solution-treated Fe-29 Mn-9 Al-C (wt%) alloys having various carbon contents leading to different volume fractions of austenite and ferrite phases were investigated. The carbon contents were 1.06%, 0.60% and 0.26%, respectively and the corresponding volume fractions of austenite were 100%, 90% and 45%, respectively. The alloy having 1.06% carbon possessed the best tensile properties but its fatigue behaviour was only comparable to the other two alloys with lower carbon contents. The alloy having 0.60% carbon possessed the lowest yield strength, but its fatigue life was slightly better than other two alloys. The alloy having 0.26% C possessed lowest elongation and medium strength, and its fatigue life was comparable to the other two alloys. Their tensile properties and fatigue behaviour were explained in terms of crack initiation, crack propagation, grain size, constituent arrangement and constituent fraction.     

Effects of samarium content on microstructure and mechanical properties of Mg–0.5Zn–0.5Zr alloy

Effects of samarium (Sm) content (0, 2.0, 3.5, 5.0, 6.5 wt%) on microstructure and mechanical properties of Mg–0.5Zn–0.5 Zr alloy under as-cast and as-extruded states were thoroughly investigated. Results indicate that grains of the as-cast alloys are gradually refined as Sm content increases. The dominant intermetallic phase changes from Mg₃Sm to Mg₄₁Sm₅ till Sm content exceeds 5.0 wt%. The dynamically precipitated intermetallic phase during hot-extrusion in all Sm-containing alloys is Mg₃Sm. The intermetallic particles induced by Sm addition could act as heterogeneous nucleation sites for dynamic recrystallization during hot extrusion. They promoted dynamic recrystallization via the particle stimulated nucleation mechanism, and resulted in weakening the basal texture in the as-extruded alloys. Sm addition can significantly enhance the strength of the as-extruded Mg–0.5Zn–0.5 Zr alloy at room temperature, with the optimal dosage of 3.5 wt%. The optimal yield strength (YS) and ultimate tensile strength (UTS) are 368 MPa and 383 MPa, which were enhanced by approximately 23.1% and 20.8% compared with the Sm-free alloy, respectively. Based on microstructural analysis, the dominant strengthening mechanisms are revealed to be grain boundary strengthening and dispersion strengthening.     

Relationship of particle stimulated nucleation,recrystallization and mechanical properties responding to Fe and Si contents in hot-extruded 7055 aluminum alloys

The variations of coarse intermetallic particles in hot-extruded 7055 aluminum alloys with 0.041 wt%Fe and 0.024 wt% Si increasing to 0.272 wt% Fe and 0.134 wt% Si were investigated.The particle stimulated nucleation(PSN) behaviors for different kind of coarse particles were detailly analyzed by EBSD.Moreover,the effect of PSN responding to Fe and Si contents on recrystallization and tensile properties of 7055 alloys was evaluated.With increasing Fe and Si contents,the size and number density of coarseη/S particles are reduced,while the number densities of coarse Al_7Cu_2 Fe and Mg_2Si particles are both increased and the coarse Al_7Cu_2 Fe particles transform from rod-like to irregular.More PSN recrystallized grains with predominant orientations deviated from the extruded fiber textures are stimulated by the irregular Al_7Cu_2 Fe and Mg_2Si particles,because a higher degree of local non-uniform deformation is produced.The rod-like Al_7Cu_2 Fe particles cause the greatest degree of local non-uniform deformation owing to the largest aspect ratio,but the shape also restricts the area of particle deformation zone(PDZ) resulting in fewer PSN recrystallized grains.The irregular η/S particles give rise to the lowest degree of local non-uniform deformation and fewest PSN recrystallized grains with the major orientations close to the extruded fiber textures.Consequently,despite the number and size of coarse η/S particles are reduced,the proportion of high angle grain boundaries(HAGBs) is increased and the extruded fiber textures are weakened with Fe and Si contents increasing,because of the increased Al_7Cu_2 Fe and Mg_2Si particles.The strength is slightly declined by the weakened 111//ED(extrusion direction) fiber texture,while the elongation is reduced for a larger number of coarse particles and more HAGBs with higher Fe and Si contents.     

Application of ultrasound for fatigue testing of lightweight alloys

The use of aluminium and magnesium alloys offers a great potential for weight reduction in automotive applications. Load-bearing car components are subjected to 10⁸ cycles and more during service, and the high-cycle fatigue properties of construction materials are therefore of great interest.
The time-saving ultrasound fatigue testing method has been used to study the fatigue properties of a high-pressure, die-cast magnesium alloy AZ91  hp and a post-forged, cast-aluminium alloy AlSi7Mg0.3 in ambient air and saltwater (5wt% sodium chloride) spray. In ambient air, fatigue cracks in AZ91  hp emanate from voids, and it is possible to correlate void areas with the numbers of cycles-to-failure. Post-forging of AlSi7Mg0.3 reduces the numbers and size of voids. The remaining small voids (void areas smaller than 9000  μm² ) do not significantly reduce lifetimes. Saltwater deteriorates the fatigue properties of both the lightweight alloys. With increasing numbers of cycles, the influence of the corrosive liquid on fatigue strength becomes more pronounced.     

Effects of Mn on fracture behaviour of DO3 Fe3Al-based intermetallic alloy

The fracture behaviour of DO3 Fe3Al-based intermetallic alloys with and without Mn (1.5 at%) were investigated by tensile tests (TT), transmission electron microscope (TEM) and scanning electron microscope (SEM). The results show that the addition of Mn could improve mechanical properties of the alloy, including room temperature ductility and high temperature strength. DO3 Fe–28Al fractured in a transgranular cleavage mode at room temperature and it gradually changed to a ductile style with temperature increasing, whereas the sample with addition of Mn fractured mainly in a mixed intergranular–transgranular cleavage mode. Three major factors are considered to have effect of Mn on fracture behaviour of the alloys: reducing grain size, promoting slip and cross slip and enhancing cleavage strength. © 1998 Chapman & Hall     

Effects of Al content on structure and mechanical properties of hot-rolled ZrTiAlV alloys

Zirconium alloys show attractive properties for astronautic applications where the most important factors are anti-irradiation, corrosion resistance, anti-oxidant, very good strength-to-weight ratio. The effects of Al content (2.2–6.9 wt%) on structure and mechanical properties of the hot-rolled ZrTiAlV alloy samples were investigated in this study. Each sample of the hot-rolled ZrTiAlV alloys with Al contents from 2.2 wt% to 5.6 wt% is composed of the α phase and β phase, meanwhile, the relative content of the α phase increased with the Al content. However, the (ZrTi)₃Al intermetallic compound was observed as the Al content increased to 6.9 wt%. Changes of phase compositions and structure with Al content distinctly affected mechanical properties of ZrTiAlV alloys. Yield strength of the alloy with 2.2 wt% Al is below 200 MPa. As Al content increased to 5.6 wt%, the yield strength, tensile strength and elongation of the examined alloy are 1088 MPa, 1256 MPa and 8%, respectively. As Al content further increased to 6.9 wt%, a rapid decrease in ductility was observed as soon as the (ZrTi)₃Al intermetallic compound precipitated. Results show that the ZrTiAlV alloys with Al contents between 3.3 wt% and 5.6 wt% have excellent mechanical properties.     

Microstructure and Mechanical Property of 2024 Aluminium Alloy Prepared by Rapid Solidification and Mechanical Milling

Rapidly solidified 2024 aluminium alloy powders were mechanically milled, then consolidated to bulk form. The microstructural changes of the powders in mechanical milling (MM) and consolidation process were characterized by X-ray diffraction analyses and transmission electron microscopy observations. The results showed that mechanical milling reduced the grain size to nanometer, dissolved the Al2Cu intermetallic compound into the aluminium matrix and produced an aluminium supersaturated solid solution. During consolidation process. the grain size increased to submicrometer, and the Al2Cu and Al2(Cu, Mg, Si, Fe, Mn) compounds precipitated owing to heating. Increasing consolidation temperature and time results in obvious grain growth and coarsening of second phase particles. The tensile yield strength of the consolidated alloy with submicrometer size grains increases with decreasing grain size, and it follows the famous HallPetch relation     

Effects of heat treatments on the microstructures and mechanical properties of Mg–3Nd–0.2Zn–0.4Zr (wt.%) alloy

Microstructure and mechanical properties of as-cast and different heat treated Mg–3Nd–0.2Zn–0.4Zr (wt.%) (NZ30K) alloys were investigated. The as-cast alloy was comprised of magnesium matrix and Mg₁₂Nd eutectic compounds. After solution treatment at 540 °C for 6 h, the eutectic compounds dissolved into the matrix and small Zr-containing particles precipitated at grain interiors. Further aging at low temperatures led to plate-shaped metastable precipitates, which strengthened the alloy. Peak-aged at 200 °C for 10–16 h, fine β″ particles with DO₁₉ structure was the dominant strengthening phase. The alloy had ultimate tensile strength (UTS) and elongation of 300–305 MPa and 11%, respectively. Aged at 250 °C for 10 h, coarse β′ particles with fcc structure was the dominant strengthening phase. The alloy showed UTS and elongation of 265 MPa and 20%, respectively. Yield strengths (YS) of these two aged conditions were in the same level, about 140 MPa. Precipitation strengthening was the largest contributor (about 60%) to the strength in these two aged conditions. The hardness of aged NZ30K alloy seemed to correspond to UTS not YS.     

Influence of small Sb nanoparticles additions on the microstructure, hardness and tensile properties of Sn–9Zn binary eutectic solder alloy

In the present study, different weight percentages of Sb nanoparticles (100–120 nm) ranging from 0 to 1.5 wt% were added to Sn–9Zn eutectic solder alloy to investigate the effect of third element addition on the microstructure, mechanical properties as well as thermal behavior of the newly developed composite solder alloys. The results indicate that the Sb nano-particle based intermetallic compounds (IMC) were found uniformly distributed, refined the microstructure and formed IMC particles in the eutectic solder alloy. After the addition of nano Sb particles in Sn–9Zn solder, fine α-Zn phase and ε-Sb₃Zn₄ IMC particles were clearly observed in the β-Sn matrix. The ε-Sb₃Zn₄ IMC particles were uniformly distributed in the β-Sn phase, which resulted in an increase in the tensile strength due to the second phase dispersion strengthening mechanism. However, in the doped Sn–9Zn/1.5Sb alloys, α-Zn phases were broken enormously, depleted and round shaped compared to the normal rod shaped α-Zn phase microstructure in plain Sn–9Zn solder. In comparison, the ε-Sb₃Zn₄ IMC particle in the doped Sn–9Zn/1.0Sb alloy were star shaped. The average tensile strength and micro-hardness of the Sb doped Sn–9Zn solder alloys were consistently higher than the plain un-doped Sn–9Zn solder. The tensile strength and the microhardness increased with increasing Sb nano-particle content, up to 1.0 wt% of Sb content, and then decreased beyond that threshold value. Consequently the percentage (%) elongation of the Sb nanoparticle doped Sn–9Zn solder decreased with increasing Sb nano-particle content, up to 1.0 wt% of Sb content, and then increased beyond that threshold value.     

Formation of intermetallic reaction layer and joining strength in nano-composite solder joint

In this study, the effects of CeO₂ nanoparticle addition on tensile strength and formation of interfacial intermetallic compound layer for lead-free Sn-3.5Ag-0.7Cu solder joint were investigated. The results showed that the thickness of intermetallic layer was decreased with increasing weight percentages of CeO₂ reinforcements, and the growth of the intermetallic layer was remarkably suppressed during isothermal aging at 150 °C. It was also found that the tensile strength of the solder joint gradually increased with the addition of CeO₂ particles, reached to the maximum value at 0.5 wt% CeO₂ and then decreased drastically with further increase in CeO₂ content. Microstructural investigation of 1 wt% CeO₂ reinforced solder joint revealed that due to particle pushing under the influence of interfacial tension between the particles and the matrix, the brittle cluster-like regions with high concentration of CeO₂ particles were formed inside the joint. These brittle clusters act as preferential site for crack initiation during tensile test which would degrade the tensile strength. Hence, based on the results obtained in this study, addition of CeO₂ particles up to 0.5 wt% provide an optimized solder joint with improved strength together with suppressed intermetallic growth and long-term reliability.     

Effect of Zn content on the microstructures and mechanical properties of laser beam-welded ZK series magnesium alloys

The effect of Zn content on the microstructures and mechanical properties of laser beam welded ZK series magnesium alloys (ZK21, ZK40, and ZK60) has been studied. Owing to the lower heat input, laser beam welding can successfully be employed to weld ZK series magnesium alloys having Zn content up to 4 wt%, which are difficult to weld by means of conventional arc welding. However, ZK60 is susceptible to solidification cracking and presents a poor weldability, which may originate from the net-like distribution of more Mg₅₁Zn₂₀ precipitates along grain boundaries (GBs) in the fusion zone (FZ). With increasing Zn content, the amount and size of precipitates along GBs in the FZ increase, and the morphology of grains in the FZ adjacent to fusion boundary changes from cellular to equiaxed dendritic. The grains in the FZ of ZK40 alloy are the finest among the three alloys, whose size is only about 4.8 μm, and the ZK40-welded joint achieves the highest ultimate tensile strength of 312 MPa, which is up to 90.4% of the base metal.     

Correlation between ultimate tensile strength and solidification microstructure for the sand cast A357 aluminium alloy

Many studies have demonstrated a relationship between secondary dendrite arm spacing (SDAS) and the mechanical behaviour of cast aluminium–silicon alloys, both for tensile and fatigue strength. SDAS is related to the solidification time and can be predicted, with a good approximation, by finite-element simulation. However, other microstructural features can affect the tensile behaviour of cast aluminium alloys such as size and morphology of the eutectic Si particles, grain size, composition and morphology of the intermetallic compounds. The present investigation was aimed at finding valuable relationships between ultimate tensile strength and the previously mentioned microstructural parameters for the sand cast A357 aluminium alloy. The microstructural characterization was carried out by optical microscopy and image analysis on more than about 2500 micrographs. Starting from the microstructural parameters and taking into account the material hardness, a relationship able to predict the ultimate tensile strength of the alloy, with an error less than 5%, was found. This relationship can be used to evaluate the local values of the UTS in complex cast components knowing only the hardness and the microstructural parameters, even in positions where the extraction of tensile specimens is not possible.     

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.     

钛氮合金的铸态组织与性能

采用熔铸工艺法制备了含氮量为0.045%～0.27%的原位自生氮化物增强钛基复合材料,分析并测试了合金的铸态组织和力学性能.研究结果表明:在Ti-N合金中,随着氮含量的增加,合金中氮化物的形态和相组成发生了明显的改变;当氮含量在0.045%～0.18%时,合金的基体为α-Ti,增强相为TiN0.3;氮含量增加到0.225%时,增强相转变为块状Ti2N;复合材料的硬度、抗压强度和弹性模量均高于纯钛基体且随着氮含量的增加而增加;当增强相由TiN0.3转变为Ti2N时,抗压强度显著增加;由压缩断口分析可知,基体为韧性断裂,随着氮含量增加合金由韧窝 解理断口向具有解理特征的脆性断裂转变.     

Mechanical behavior and wear characteristics of fine grained ZE41 magnesium alloy

ZE41 magnesium alloy was successfully produced by friction stir processing and grain refinement was achieved from a starting size of 107 μm±6.7 μm to 3.5 μm±1.5 μm. MgZn intermetallic which was appeared as network like structure at the grain boundaries before friction stir processing was greatly affected due to the severe plastic deformation and broken as small particles as observed from the microstructural studies. Higher hardness (≈30 %) was measured for the fine grained ZE41 magnesium alloy compared with the base alloy due to the grain refinement. From the tensile tests, yield strength and ultimate tensile strength was significantly increased at the cost of decreased ductility reflected in lower strain for the fine grained ZE41 compared with the base alloy. Wear studies showed higher coefficient of friction and lower mass loss for the grain refined ZE41 magnesium alloy. From the results, it can be understood that the grain refinement achieved by friction stir processing has a profound influence on enhancing the mechanical and tribological properties of ZE41 magnesium alloy.     

Grain size effects on the mechanical properties of some squeeze cast light alloys

Mechanical property-grain size relationships have been examined for squeeze cast Al-4.5% Cu alloy, for an aluminium alloy with a composition corresponding to wrought 7010, and for a magnesium alloy AZ91. The general trend of the results obtained showed that the tensile properties and the fatigue strength improved as grain size decreased and the reverse was found to be the case for the fatigue crack propagation resistance and fracture energy of these castings. However, the results also showed that no simple common relationship existed between grain size and the tensile properties of the different alloys. The results are discussed in respect of their microstructures.     

Influence of matrix structure on the fatigue properties of an alloyed ductile iron

Rotary bending fatigue tests were conducted on ductile iron containing 1.25 wt% nickel, 1.03 wt% copper and 0.18 wt% molybdenum with various matrix structures. Several heat treatments were applied to obtain ferritic, pearlitic/ferritic, pearlitic, tempered martensitic, lower and upper ausferritic structures in the matrix of a pearlitic as-cast alloyed ductile iron. The tensile properties (ultimate tensile strength, 0.2% yield strength and percent elongation), the hardness and the microstructures of the matrixes were also investigated in addition to fatigue properties. Fractured surfaces of the fatigue specimens were examined by the scanning electron microscope. The results showed that the lowest hardness, tensile and fatigue properties were obtained for the ferritic structure and the values of these properties seemed to increase with rising pearlite content in the matrix. While the lower ausferritic structure had the highest fatigue strength, the upper ausferritic one showed low fatigue and tensile properties due to the formation of the second reaction during the austempering process.     

Microstructure,tensile properties,and creep behavior of high-pressure die-cast Mg–4Al–4RE–0.4Mn (RE = La,Ce) alloys

High-pressure die-cast (HPDC) Mg–4Al–4RE–0.4Mn (RE = La, Ce) magnesium alloys were prepared and their microstructures, tensile properties, and creep behavior have been investigated in detail. The results show that two binary Al–Ce phases, Al₁₁Ce₃ and Al₂Ce, are formed mainly along grain boundaries in Mg–4Al–4Ce–0.4Mn alloy, while the phase composition of Mg–4Al–4La–0.4Mn alloy contains only α-Mg and Al₁₁La₃. The Al₁₁La₃ phase comprises large coverage of the grain boundary region and complicated morphologies. Compared with Al₁₁Ce₃ phase, the higher volume fraction and better thermal stability of Al₁₁La₃ have resulted in better-fortified grain boundaries of the Mg–4Al–4La–0.4Mn alloy. Thus higher tensile strength and creep resistance could be obtained in Mg–4Al–4La–0.4Mn alloy in comparison with that of Mg–4Al–4Ce–0.4Mn. Results of the theoretical calculation that the stability of Al₁₁La₃ is the highest among four Al–RE intermetallic compounds supports the experimental results further.     

Effect of cobalt additions on the age hardening of Cu-4.5Ti alloy

The effects of 0.9 and 1.8 wt% cobalt additions on the age hardening behaviour of Cu-4.5Ti alloy have been investigated. It has been observed that though Co addition results in the refinement of grain size and the Cu-Ti-Co alloys exhibit age hardening (giving rise to peak hardness on aging at 400°C for 16 hours), the peak hardness as well as the corresponding yield and tensile strengths were found to decrease with increasing cobalt content. The electrical conductivities of 0.9 and 1.8 wt% Co alloys were found to be 6% and 10% International Annealed Copper Standard (IACS) and 7% and 14% IACS in solution treated and peak aged conditions, respectively. Like in the binary Cu-Ti alloys, precipitation of ordered, metastable and coherent Cu₄Ti(¹) precipitate was found to be responsible for maximum strengthening in these alloys. In addition, coarse intermetallic phases of Ti and Co, viz. Ti₂Co and TiCo particles have been observed in all the conditions studied. The inferior mechanical properties of Cu-Ti-Co alloys compared with those of the binary Cu-Ti alloys are attributed to the depletion of Ti from matrix, which is consumed to form Ti₂Co and TiCo phases.