Effect of sintering temperature on microstructures and mechanical properties of ZK60 magnesium alloys

In this study, ZK60 Mg alloys were prepared via hot-press sintering under a constant pressure of 30 MPa as well as Ar atmosphere. The sintering temperature was determined to be in the range of 450–600 °C with an interval of 50 °C. The effect of sintering temperature on the microstructures and mechanical properties of the alloys was investigated. All the four sintered alloys mainly exhibited an α-Mg-phase structure and equiaxed grain microstructure. However, a specific amount of melt, enriched in Zn element, formed when the sintering temperature reached 500 °C. Thus, only the alloy sintered at 450 °C maintained the nominal composition of the alloy powder, and exhibited the favorable yield strength and hardness, which was 135.1 MPa and 57 HV, respectively. The alloys sintered at 550 °C and 600 °C exhibited a reduced yield strength and hardness due to the loss of Zn element.

Effects of Ce Addition on Solidification Structure of a Low-Carbon 42CrMo4 Steel

Effects of Cerium (Ce) addition on solidification structure of a low-carbon 42CrMo4 steel was investigated. The addition of up to 0.067 wt.% of Ce in the steel produced greatly improved solidification structure with a suppressed columnar grain zone, finer grain size in an equiaxed grain zone and zero area fraction of casting shrinkage cavity. The added Ce occurred in the steel both in the form of Ce oxy-sulfide inclusions and as dissolved atomic Ce segregated together with other elements at prior austenite grain boundaries and at interdendritic spacing. The Ce oxy-sulfide inclusions were found to play a major role in the observed improved grain structure meanwhile dissolved Ce had pronounced effects on morphology of dendritic networks. The fraction of Ce dissolved in the melt appeared to bring about increase in fluidity of the molten steel, leading to total elimination of interdendritic shrinkage porosity in solidification structure of the steel with added Ce. Ce addition can be considered as a potential solution for grain structure refinement in heavy-weight castings of 42CrMo4 steel grade.

High Strain Rate Response of In-Situ TiB2/7055 Composite by Taylor Impact

The high strain rate deformation behavior and microstructure evolution of in situ TiB2 particle reinforced Al-Zn-Mg-Cu composite were investigated by means of Taylor impact. The dynamic tests were performed at three different impact velocities. Under three different velocities, no obvious shear failure occurred in the composite, indicating a good impact resistance. Compared to the quasi-static compression test, the dynamic yield strength increased obviously with the rise of velocity, even more than 1 GPa. The dislocation multiplication, phonon drag effect and ceramic reinforcement increased the flow stress of composite. Fine, equiaxed grain structure developed after impact, resulting from grain fragmentation or dynamic recrystallization. Finite element simulation of Taylor impact was qualitatively in agreement with the experiments, which was useful to elucidate the formation of equiaxed grain structure.

A comparison study of microstructure, texture and mechanical properties between two 6xxx aluminum alloys

This paper investigates a comparison study of microstructure, texture and mechanical properties between two 6xxx aluminum alloys through microstructure, texture characterization and tensile test. The results show that they exhibit different microstructure, texture and mechanical properties. In comparison with the alloy sheet with a low weight ratio of Mg to Si (Si-excess), the alloy sheet with a higher weight ratio of Mg to Si (Mg-excess) and additional Zn possesses the finer as-casting and solution treated equiaxed grain structure, less particles with larger size before solution treatment, weaker recrystallization texture mainly including Cube {001}<100> orientation and weaker mechanical properties. The low weight ratio of Mg to Si corresponds to slightly higher yield strength and ultimate tensile strength, but much higher plastic strain ration r, work hardening exponent n values and elongation. Interestingly, Portevin-Le Chatelier (PLC) effect is very prevailed in the alloy sheet with a higher weight ratio of Mg to Si and additional Zn, which is responsible for the low elongation and r value. The alloy containing a low weight ratio of Mg to Si may be beneficial to improve comprehensive mechanical property.

Microstructure and Mechanical Properties of Silicon Carbide-Treated Ferritic Stainless Steel Welds

To further previous works on grain refinement in ferritic stainless steel (FSS) welds via elemental powder addition, microstructure evolution and mechanical properties in non-metallic carbide treated FSS weld is discussed. Silicon carbide (SiC) powder preplaced on medium chromium FSS bevelled joint was fusion melted using tungsten inert gas (TIG) torch at different combination of process parameters. The incorporation of the powder in the weld pool constricted the weld geometry in addition to grain modification from columnar to equiaxed grain structure. Whilst significant improvement was obtained in hardness characteristics in powder treated welds, those of ductility and tensile strength were marginal. The study also established that welds mechanical properties are controlled by a combination of phenomena such as phase fraction and grain morphology.

The Microstructure and Properties of Low Carbon PM 625 Alloy for Marine-Based Application

The low carbon content powder metallurgy (PM) 625 alloy were manufactured by vacuum induction gas atomization (VIGA) and hot isostatically pressing (HIP) for marine-based application such as parts in the subsea Xmas tree. Corrosion experiment was performed in simulated deep seawater and subsea oil & gas service environment. The microstructures and properties of low carbon 625 alloy were comparably investigated with that of the as-cast alloy. The results indicated that the dendritic arm spacing (DAS) of the as-cast 625 alloy is 2 orders of magnitude higher than that of the powders, whereas the HIPed alloys possess a fine equiaxed grain structures without dendritic segregation and an average grain size of 14.5μm. No minor phase has been found beside the γ matrix in the original powders with different particle size. The tensile strength of low carbon PM 625 alloy is 26% higher than that of as-cast 625 alloy. PM 625 alloy possesses an excellent corrosion resistant in simulated deep seawater and oil & gas service environment for 30 days.