Effects of Fe content on the microstructure and properties of CuN i10FeM n1 alloy tubes fabricated by HCCM horizontal continuous casting

Heating-cooling combined mold（HCCM） horizontal continuous casting technology developed by our research group was used to produce high axial columnar-grained CuN i10 FeM n1 alloy tubes with different Fe contents. The effects of Fe content（1.08wt%–2.01wt%） on the microstructure, segregation, and flushing corrosion resistance in simulated flowing seawater as well as the mechanical properties of the alloy tubes were investigated. The results show that when the Fe content is increased from 1.08wt% to 2.01wt%, the segregation degree of Ni and Fe elements increases, and the segregation coefficient of Ni and Fe elements falls from 0.92 to 0.70 and from 0.92 to 0.63, respectively. With increasing Fe content, the corrosion rate of the alloy decreases initially and then increases. When the Fe content is 1.83wt%, the corrosion rate approaches the minimum and dense, less-defect corrosion films, which contain rich Ni and Fe elements, form on the surface of the alloy; these films effectively protect the α-matrix and reduce the corrosion rate. When the Fe content is increased from 1.08wt% to 2.01wt%, the tensile strength of the alloy tube increases from 204 MPa to 236 MPa, while the elongation to failure changes slightly about 46%, indicating the excellent workability of the CuNi10FeMn1 alloy tubes.

Effect of continuous induction annealing on the microstructure and mechanical properties of copper-clad aluminum flat bars

Copper-clad aluminum （CCA） flat bars produced by the continuous casting-rolling process were subjected to continuous induction heating annealing （CIHA）, and the effects of induction heating temperature and holding time on the microstructure, interface, and mechanical properties of the fiat bars were investigated. The results showed that complete recrystallization of the copper sheath occurred under CIHA at 460℃ for 5 s, 480℃ for 3 s, or 500℃ for 1 s and that the average grain size in the copper sheath was approximately 10.0 μm. In the case of specimens subjected to CIHA at 460-500℃ for longer than 1 s, complete recrystallization occurred in the aluminum core. In the case of CIHA at 460-500℃ for 1-5 s, a continuous interracial layer with a thickness of 2.5-5.5 μm formed and the thickness mainly increased with increasing annealing temperature. After CIHA, the interracial layer consisted primarily of a Cu9A14 layer and a CuA12 layer; the average interface shear strength of the CCA flat bars treated by CIHA at 460-500℃ for 1-5 s was 45-52 MPa. After full softening annealing, the hardness values of the copper sheath and the aluminum core were HV 65 and HV 24, respectively, and the hardness along the cross section of the CCA flat bar was uniform.

Effect of compression direction on the dynamic recrystallization behavior of continuous columnar-grained CuNi10Fe1Mn alloy

The dynamic recrystallization（DRX） behavior of continuous columnar-grained（CCG） Cu Ni10Fe1 Mn alloy was investigated by hot compression along the solidification direction（SD） and perpendicular to the solidification direction（PD）. Specimens were compressed to a true strain of 0.8 at temperatures ranging from 25°C to 900°C and strain rates ranging from 0.01 to 10 s-1. The results indicate that DRX nucleation at grain boundaries（GBs） and DRX nucleation at slip bands（SBs） are the two main nucleation modes. For SD specimens, C-shaped bending and zig-zagging of the GBs occurred during hot compression, which made DRX nucleation at the GBs easier than that at the SBs. When ln Z ≤ 37.4（Z is the Zener–Hollomon parameter）, DRX can occur in SD specimens with a critical temperature for the DRX onset of;50°C and a thermal activated energy（Q） of 313.5 k J·mol-1. In contrast, in PD specimens, the GBs remained straight, and DRX nucleation occurred preferentially at the SBs. For PD specimens, the critical temperature is about 700°C, Q is 351.7 k J·mol-1, and the occurrence condition of DRX is ln Z ≤ 40.1. The zig-zagging of GB morphology can significantly reduce the nucleation energy at the GBs; as a result, DRX nucleation occurs more easily in SD specimens than in PD specimens.

Effect of post-weld heat treatment on microstructure and properties of Ti-23Al-17Nb alloy laser beam welding joints

The mechanical properties of Ti-23Al-17Nb (mole fraction,%) laser beam welding alloy joint at room temperature are comparable to that of the base materials.However,the strength and ductility of the as-welded joint deteriorate seriously after high temperature circulation.The effect of post-welded heat treatment on the microstructure and mechanical properties of the joint was investigated.The heat treatment was taken at 980 ℃ for 1.5 h,then furnace cooling and air cooling were performed separately.The results indicate that proper post-welded heat treatment improves the ductility of the joint at high temperature.

Microstructure and texture evolution of Mg–3Zn–1Al magnesium alloy during large-strain electroplastic rolling

Large-strain deformation by single electroplastic rolling （EPR） was imposed on AZ31 magnesium alloy strips. During EPR at low temperature （150-250℃）, numerous twins formed in the alloy. After EPR at a high temperature （350℃）, the number of twins reduced and some dynamic recrystallization （DRX） grains formed at grain boundaries and twinned regions. The synergic thermal and athermal effects generated by electropulsing, which promoted dislocation motion, induced a few small DRX grains, and ductile bandings were mainly re- sponsible for large-strain deformation during EPR. The inclination angle of the basal pole stemmed from the counterbalance of the inclina- tion direction of the basal pole between the DRX grains and deformed coarse grains.

Simulation of Magnesium Alloy AZ91D Microstructure Using Modified Cellular Automaton Method

A two-dimensional modified cellular automaton model was developed to simulate the solidification process of magnesium alloy. The stochastic nucleation, solute redistribution, and growth anisotropy effects were taken into account in the present model. The model was used to simulate the grain size of magnesium alloy AZ91D for various cooling rates during the solidification process. To quantitatively validate the current model, metallographic experiments were carried out on specimens obtained from sand mold AZ91D step castings. The metallographic results agree well with the prediction results. The current model can be used to accurately predict the grain sizes of cast AZ91D magnesium alloy.

Bending Properties and Fracture Behavior of Ti-23Al-17Nb Alloy Laser Beam Welding Joints

Ti-23Al-17Nb alloy is an important high temperature structural material used in the space and aerospace fields. Welding of this alloy is an indispensable processing method, so the microstructures and mechanical properties of these welded joints must be studied to improve the welds. Longitudinal three-point bending tests were conducted to measure the bending ductility of laser beam welded joints. The crack distribution and fracture surface were investigated to further analyze the fracture behavior. The results indicate that the bending ductility decreases as the heat input by the laser beam welding increases. The crack inducing strain reaches 4.24%, while the fracturing strain exceeds 5% when the heat input is below 316 J/cm. If the columnar crystal grain of the weld metal exhibits a uniform orientation, the bending ductility is worse. The fractography analysis shows that the cracking propagates transgranularly and the fracture surface has a cleavage mode.

Thermal Stresses in a Cylinder Block Casting Due to Coupled Thermal and Mechanical Effects

Thermal stress in castings results from nonuniform cooling. The thermal stress and the deformation can change the casting and mold contact conditions which then alter the heat transfer between the casting and the mold. The contact element method was used to study the interaction between a sand mold and a casting. The contact status was then fed back to the heat transfer analysis between the sand mold and the casting to re-evaluate the heat transfer coefficient based on the gap size or pressure between surfaces. The thermal and mechanical phenomena are then coupled in two directions. The method was applied to analyze stress in a stress frame specimen casting and a cylinder block. The results are more accurate than without consideration of the contact effects on the heat transfer.