Tri-modal microstructure is often the target microstructure of titanium alloy components. In this study, the parameters, such as volume fraction, size of primary equiaxed α (α_p), secondary lamellar α (α_s) and thin α plates (α_t) in tri-modal microstructure of Ti-6Al-2Zr-1Mo-1V alloy are adjusted by double heat treatment procedures. The properties of these constituent phases and their effect on the macro-properties are then investigated. The results show that the hardness of primary α (α_p) varies slightly with heat treatment routes. The hardness of α plates region including α_s and α_t increases with increasing α_t volume fraction and not with decreasing thickness of α_s and α_t. Using volume average of the thickness of α_s and α_t as effective thickness (t_eff), the hardness of α plates region and t_eff follow the Hall-Petch relationship. Meanwhile, as α_t volume fraction increases, colony structure of α_s is gradually destroyed, which makes each α_s have large deformation degree by multiple directions slip. When volume fraction ratio of α_p, α_s and α_t is about 1:1:1, α_p and α_s can undergo relatively large deformation and α_t can contribute relatively large strength to the alloy and therefore the alloy has both good strength and ductility.

The effects of Ce and In on microstructure and corrosion properties of Zn-9Al-2.5Mg had been investigated in this research. The corrosion product morphology and the corrosion mechanism were observed and discussed. The microstructure and the corrosion product morphology were seen by OEM and SEM respectively. The phases were determined by XRD and the elements in micro region were used by EDS. The corrosion behavior was determined by full immersion corrosion method and electrochemical test method. Results show that the phases of Zn-9Al-2.5Mg alloy are constituted by Zn-rich solid solution, Al-rich solid solution and ternary eutectic structure (Zn-Al-MgZn2/Mg2Zn11). After adding 0.1% Ce, the grain size of the Zn-9Al-2.5Mg alloy is obviously refined. After adding 0.1%Ce and 0.05%In, the amount of Al-rich solid solution is inhibited and dendritic Zn-rich solid solution increased. The amount of ternary eutectic structure (Zn-Al-MgZn2/Mg2Zn11) decreases gradually. Compared with Zn-9Al-2.5Mg alloy, the corrosion potential of Zn-9Al-2.5Mg-0.1Ce increased slightly and the corrosion current density is basically unchanged, which remains at 5.97x10-6 A/cm2. It's half the corrosion rate of pure Zn. When the content of In increases from 0.05% to 0.1%, the current density increases from 8.71x10-6 A/cm2 to 20.42x10-6 A/cm2. The corrosion products of pure Zn and Zn-9Al-2.5Mg alloys are Zn5(OH)6(CO3)2 and Zn5(OH)8ClH2O, Which present sphere (petal and rod) assembly structure. The difference is that the formation of Zn-Al and Mg-Al layered double hydroxides (Zn4Al2(OH)12CO33H2O and Mg6Al2(OH)16CO34H2O)-LDH are observed for Zn-9Al-2.5Mg alloys. After adding Ce to Zn-9Al-2.5Mg alloy, the LDH film is rather compact. But the LDH film is thin and floccus after In added. It leads to a lower resistance of corrosion products and accelerate the corrosion process. Keywords: Zn-Al-Mg alloy, Trace element, Corrosion mechanism

The effects of Ce on the microstructure of Zn-5.5Al-4.5Mg alloy and the corrosion mechanism of Zn-5.5Al-4.5Mg-0.3Ce alloy and its coatings were investigated in this research. The results show that the structure of Zn-5.5Al-4.5Mg-0.3Ce alloy is composed of hcp-Zn, fcc-Al and ternary eutectic structure (Zn/Al/MgZn₂/Mg₂Zn₁₁), without dendritic tissue and MgZn₂. The salt spray corrosion performance of Zn-5.5Al-4.5Mg-0.5CMC-2C coating was significantly better than that of Zn-5.5Al-4.5Mg-0.3Ce coating and Zn-5.5Al-4.5Mg-0.5CMC coating. The corrosion current density of Zn-5.5Al-4.5Mg-0.5CMC-2C coating was 3.217 μA cm⁻², which was significantly lower than 3.96 μA cm⁻² of Zn-5.5Al-4.5Mg-0.3Ce alloy and 5.879 μA cm⁻² of Zn-5.5Al-4.5Mg alloy. Sodium carboxymethylcellulose and graphene improve the film formation and electrical conductivity of water-based lithium silicate resin. During corrosion of Zn-5.5Al-4.5Mg-0.3 Ce series alloy and coatings, Zn and Mg₂Zn₁₁ dissolved preferentially to form corrosion products of Zn₅(OH)₆(CO₃)₂ and Zn₅(OH)₈Cl₂·H₂O. Mg₆Al₂(OH)₁₆CO₃·4H₂O and Zn₄Al₂(OH)₁₂CO₃·3H₂O bimetallic hydroxide colloidal membranes were formed, which attached and wrapped on the surface of early corrosion products. Mg₆Al₂(OH)₁₆CO₃·4H₂O and Zn₄Al₂(OH)₁₂CO₃·3H₂O, preventing the dissolution of soluble corrosion products, improved the corrosion resistance of Zn-5.5Al-4.5Mg-0.3Ce alloy.

The oxidation resistance of Zn-9Al-2.5Mg-xBe (x = 0,0.005,0.01,0.05,0.1) alloys was investigated in this study through isothermal oxidation experiments. The alloy microstructure, morphology, and composition of the oxide film were analyzed using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and x-ray diffraction (XRD). The oxidation kinetics and thermodynamics of Zn-9Al-2.5Mg were calculated, and the oxidation mechanism was discussed. The results show that the Zn-9Al-2.5Mg-0.05Be alloy exhibits a fine dendritic microstructure, with a large quantity of Zn-MgZn₂ binary eutectic and Zn-Al-MgZn₂/Mg₂Zn₁₁ ternary eutectic phases uniformly distributed. The Zn-9Al-2.5Mg-0.05Be alloy has the lowest oxidation rate among the tested alloys, with an oxide weight gain of 12 mg m⁻², which is only 0.67 times that of the Zn-9Al-2.5Mg alloy. The oxide film on the surface of the alloy is relatively dense and maintains the appearance of the metal. The main constituents of the oxide film are Zn, Al, Mg₁₇Al₁₂, Mg₂Zn₁₁, and BeO, with no formation of Al₂O₃ or MgO. The oxidation mechanism of the Zn-9Al-2.5Mg-0.05Be alloy is attributed to the reaction of Be with oxygen, forming BeO, or the displacement reaction of Be with Al₂O₃ and MgO to form BeO, which inhibits the formation of Al₂O₃ and MgO.

Fe-Cr-C-based coatings were fabricated on Q690 steel via ultrasonic vibration-assisted plasma cladding at varying ultrasonic powers (0–65 W) with a fixed frequency of 18.5 kHz. The coatings primarily consisted of martensite, retained austenite, and (Cr,Fe)₇C₃ carbides, along with (Cr,Fe,Mo)-B borides along grain boundaries. Increasing ultrasonic power promoted cavitation and acoustic streaming, which refined columnar dendrites, reduced elemental segregation (notably for B and Mo), and increased the fraction of fine equiaxed grains without altering phase composition. As a result, the average microhardness increased from 797.1 to 828.5 HV0.1. The friction coefficient decreased from 0.675 to 0.626, while the wear-track width, wear depth, and wear mass loss decreased from 4.0 mm to 2.5 mm, from 112.5 μm to 32.4 μm, and from 20.40 mg to 4.75 mg, respectively. The wear mechanism shifted from severe adhesive wear to mild abrasive wear. These results demonstrate that increasing ultrasonic vibration power effectively refines the solidification microstructure and significantly improves the hardness and wear resistance of plasma-clad Fe-Cr-C-based coatings.