Effect of Equivalent Stress Amplitude on Multiaxial Fretting Fatigue Behavior of Al–Zn–Mg Alloy

Strength of Materials - The fretting fatigue behavior in Al–Zn–Mg alloy is investigated under conditions of various equivalent stress amplitudes of cyclic multiaxial loadings and the...     

Hot Extrusion Effect on the Microstructure and Mechanical Properties of a Mg–Y–Nd–Zr Alloy

Strength of Materials - Mg–Zn–Y–Nd alloy was prepared by casting and hot extrusion. The microstructure and mechanical properties of OM, SEM, XRD, TEM, and tensile tests were...     

Effect of Si content on microstructure and mechanical properties of Al–Si–Mg alloys

Microstructure and mechanical properties of as-cast and as-extruded Al–Si–Mg alloys with different Si content are investigated by tensile test, microstructure observation. High density of Si particles in the Al alloys can induce dynamic recrystallization during hot extrusion and it becomes more matured with an increase in the density of Si particles. The tensile strength of as-cast and as-extruded alloys can be improved with the increase of Si content and hot extrusion make the elongation of alloys increase dramatically. Considerable grain refining effect caused by recrystallization occurred during hot extrusion of S2 (equivalently commercial A356 alloy) and S3 (near eutectic alloy) alloys plays an important role in the improvement of elongation. A good combination of strength and elongation for the as-extruded S3 alloy indicates that near eutectic Al–Si alloys can be hot-extruded to produce aluminum profiles with high performance.     

Effect of cooling rate and Mg content on the Al–Si eutectic for Al–Si–Cu–Mg alloys

This study investigates and clarifies the qualitative and quantitative effects of Mg content and cooling rate (ranging from 0.5 to 4 °C/s), on the modification of the silicon eutectic structure and on the undercooling of the silicon eutectic growth temperature (ΔT_Si-eut) in the series of Al–Si–Cu–Mg alloys. The critical Mg content to produce a notable improvement in the silicon eutectic by 1.5 modification levels (regardless of the cooling rate) is 0.6 wt.% Mg. A similar increase in the modification level was also observed when the cooling rate was increased to a maximum of 4 °C/s, regardless of the Mg content. Measurements of the area and roundness of the silicon particles showed a good correlation with the modification level. The undercooling (ΔT_Si-eut) increased by up to ~ 23 °C at a relatively high Mg content and cooling rate and up to ~ 14 °C when the Mg content was increased from 0.4 to 0.6 wt.%.     

Effect of Icosahedral Phase on Crystallographic Texture and Mechanical Anisotropy of Mg–4%Li Based Alloys

Through investigating and comparing the microstructure and mechanical properties of the as-extruded Mg alloys Mg–4%Li and Mg–4%Li–6%Zn–1.2%Y(in wt%), it demonstrates that although the formation of I-phase(Mg_3Zn_6Y, icosahedral structure) could weaken the crystallographic texture and improve the mechanical strength, the mechanical anisotropy in terms of strength remains in Mg–4%Li–6%Zn–1.2%Y alloy.Failure analysis indicates that for the Mg–4%Li alloy, the fracture surfaces of the tensile samples tested along transverse direction(TD) contain a large number of plastic dimples, whereas the fracture surface exhibits quasi-cleavage characteristic when tensile samples were tested along extrusion direction(ED).For the Mg–4%Li–6%Zn–1.2%Y alloy, typical ductile fracture surfaces can be observed in both TD andED samples. Moreover, due to the zonal distribution of broken I-phase particles, the fracture surface of TD samples is characterized by the typical woody fracture.     

Effect of Sheet Configuration on Microstructure and Mechanical Behaviors of Dissimilar Al–Mg–Si/Al–Zn–Mg Aluminum Alloys Friction Stir Welding Joints

Friction stir welding(FSW) was used to weld dissimilar Al–Mg–Si/Al–Zn–Mg aluminum alloys in this work.Influences of sheet configuration on microstructure and mechanical properties of the joints were mainly discussed.Results showed that rather different joint cross sections were obtained when using different sheet configurations.Coarser β' phases can be observed at the heat affected zone(HAZ) of the Al–Mg–Si alloy side,which was the main factor affecting the tensile properties and the fatigue properties.Tensile strengths of the dissimilar Al–Mg–Si/Al–Zn–Mg joints using both configurations were higher than that of the Al–Mg–Si FSW joint.When the Al–Zn–Mg alloy was located at the advancing side(AS),the joints owned better fatigue properties due to the bridging effect of the big secondary phase particles.     

Effect of Different Aging Processes on the Microstructure and Mechanical Properties of a Novel Al–Cu–Li Alloy

The effects of different aging processes on the microstructure and mechanical properties of a novel Al–Cu–Li alloy have been investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It is found that the tensile properties of a novel Al–Cu–Li alloy are sensitive to aging processes, which correspond to different microstructures. σ(Al_5Cu_6Mg_2) and T_1(Al_2CuLi) phases are the major precipitates for the alloy in T6 aging condition(165 ℃/60 h). After duplex aging condition(150 ℃/24 h + 180 ℃/12 h), σ, θ'(Al_2Cu) and T_1 phases are detected. Only the T_1 phases can be found in the T8 state alloy(6% pre-strain+135 ℃/60 h). The failure modes of alloy in T6 and duplex aging conditions are dimple-intergranular fracture, while typical quasi-cleavage fracture in T8 condition.     

Effects of Ag Addition on Precipitation and Fatigue Crack Propagation Behavior of a Medium-Strength Al–Zn–Mg Alloy

Effects of trace addition of Ag on the fatigue crack propagation behavior and microstructure of a mediumstrength aged Al–Zn–Mg alloy were investigated in the present work. The results show that a combination of enhanced tensile strength and improved fatigue crack propagation resistance in Al–Zn–Mg alloys is achieved with small addition of Ag. The enhanced strength is attributed to the high density of η’ precipitates within the grains and narrow precipitate free zones in the vicinity of grain boundaries. The main contribution to the improvement of fatigue crack propagation resistance comes from the coarser precipitates within the grains. When subjected to two-step aging, Ag-added alloy shows larger semi-coherent matrix precipitates. These relatively coarser precipitates increase the homogeneity of deformation and therefore improve the fatigue crack propagation resistance. In addition, microstructure analysis indicates that the size and distribution of inclusions as well as the grain structures of Al–Zn–Mg alloys are independent of Ag addition.     

Effect of microstructure on fatigue behaviour of cast Al–7Si–Mg alloy

Abstract

The fatigue behaviour of a cast Al–7Si–Mg alloy, conforming to A356, has been studied. Specimens of this material were tested in both the as cast condition and a solution treated and aged condition. It was observed that the size, number, and position of casting defects influenced the fatigue life very strongly. This marked effect nearly hides that of the heat treatment. Nevertheless, if the analysis is carried out considering only results obtained from sound specimens it is revealed that the heat treatment causes an improvement in the fatigue resistance of the alloy.     

Effect of Porosity on Thermal Conductivity of Al–Si–Fe–X Alloy Powder Compacts

The thermal conductivity and thermal diffusivity of hot- and cold-pressed Al–17Si–5Fe–3.5Cu–1.1Mg–0.6Zr (mass%) alloy powder compacts were investigated as a function of the porosity volume fraction. Samples with a very low degree of porosity were produced by hot-pressing air atomized alloy powder with a particle size of 45–100 m. The same powder was used to produce highly porous compacts by cold compaction using a manual press. The thermal diffusivity of the powder compacts was measured using a sinusoidal modulation photopyroelectric technique in a configuration that is similar to the laser flash method. The thermal diffusivity of the material decreases by a factor of about 13 with an increasing porosity of 25 vol% and a factor of about 300 at 60 vol % porosity. Since the calculated specific heat (weighted average of mass specific heat values of major alloy compounds) is much less porosity dependent, the porosity dependence of the thermal conductivity is similar to the thermal diffusivity and decreases exponentially with increasing porosity. Microstructural characterization of high porosity samples prepared by cold compaction indicated that the distribution of pores is not uniform over the cross-section. An interconnecting network of open and closed pores in the form of channels created pockets of porosity,clearpage 2.3pc which are largely responsible for a drastic reduction of thermal conductivity 4pc with increasing porosity.     

Mechanical Alloying Effect on the Structure of Fe-Al-(Si) Alloy

The mechanical alloying effects on the structures of Fe71.3AI28.4(CeO2)0.3 and Fe73.3AI9.8-Si,e.e(CeO2)0.3 samples have been investigated mainly by Mossbauer spectroscopy and X-ray diffraction. It is found that with the increase of milling time, a substituting disordered a-Fe solution is formed gradually and almost completed after milled for 72 h. Further increasing milling time causes the atomic rearrangement within the powders. Correspondingly' the average lattice parameter and average crystalline size change until 72 h and remain constant after 72 h. The addition of Si leads to the higher disordered degree reflected in the smaller average hyperfine field and larger mean Square deviation.     

Effect of Twin Boundary–Dislocation–Solute Interaction on Detwinning in a Mg–3Al–1Zn Alloy

In the present study,the influence of solute atoms together with dislocations at {1012} twin boundary(TB) on mechanical behavior of a detwinning predominant deformation in a Mg alloy AZ31 plate was systematically studied.The results show that a large number of {1012} twins disappear during recompression along the normal direction.Both the TB–dislocation interaction and TB–solute–dislocation interaction can greatly enhance the yield stress of the recompression along the normal direction(ND).However,the solute segregation at {1012} TBs with an intensive interaction with a dislocations cannot further enhance the yield stress of ND recompression.The samples with TB–dislocation interaction show a similar working hardening performance with that subjected to a TB–solute–dislocation interaction.Both the TB–dislocation interaction and TB–solute–dislocation interaction greatly reduce the value of work hardening peaks during a detwinning predominant deformation.     

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.     

Microstructural characterization of Mg–Al–Sr alloys

The microstructural details of fourteen Mg–Al–Sr alloys were investigated in the as-cast form by a combination of scanning electron microscopy/energy dispersive spectrometer (SEM/EDS) analysis and quantitative electron probe microanalysis (EPMA). The heat transfer method coupled with the DSC measurement has been utilized to determine the solidification curves of the alloys. The morphology and the chemical composition of the phases were characterized. The microstructure of the alloys is primarily dominated by (Mg) and (Al₄Sr). In the present investigation, ternary solid solubility of three binary compounds extended into the ternary system has been reported and denoted as: (Al₄Sr), (Mg₁₇Sr₂) and (Mg₃₈Sr₉). The (Al₄Sr) phase is a substitutional solid solution represented by Mg_xAl_4–xSr and has a plate-like structure. The maximum solubility of Al in Mg₁₇Sr₂ was found to be 21.3 at%. It was also observed that Mg₃₈Sr₉ dissolved 12.5 at% Al.     

Effect of Microstructures on Mechanical Properties of Ti–6.5Al–2Sn–4Zr–4Mo–1W–0.2Si Alloy

The tensile properties at both room temperature and 550 °C are investigated in Ti – 6.5Al – 2Sn – 4Zr – 4Mo – 1W – 0.2Si with three typical microstructures, which are lamellar, bimodal, and equiaxed microstructures. The results show that the yield and ultimate tensile strengths decrease while the ductility increases as the volume fraction of primary α phase increases at both temperatures. The above phenomena result from the decrease in the β transformed microstructure, which consists of fine α and β lamellae with high-density α/β interfaces blocking dislocation slipping. The yield and ultimate tensile strengths at 550 °C are lower than that at room temperature, and the ductility at 550 °C is higher than that at room temperature, both of which are attributed to the activity of multislipping systems at high temperature.