Effect of Friction Stir Processing at High Rotational Speed on Aging of a HPDC Mg9Al1Zn

Friction stir processing (FSP) has confirmed its valuable contribution to refining microstructures and the improvement of mechanical properties for Mg-Al alloys. Reference papers illustrate that post-processing aging treatments enhance hardness, but with the application of a solution heat treatment prior to FSP. In this work, aging was performed at two different temperatures (170 and 300 °C) directly on friction stir processed samples of AZ91 produced using high pressure die casting (HPDC). High rotational speeds of the tools (2500 and 3000 rpm) increases the heat input and the temperature of the plates during the process up to 270 °C. Vickers microhardness (HV) increased by 15–20% in the nugget, compared to the as FSPed condition; moreover, a greater homogeneity of hardness values was found at the higher aging temperature used. The β-Mg17Al12 precipitates are randomly distributed inside grains of the stirred area, while in the thermomechanical affected zone (TMAZ) they have grown in a network similar to the old eutectic. A preliminary investigation of FSPed samples deformed at 300 °C found that an equivalent hardness increase is achievable using hot deformation due to dynamic precipitation; to find local homogeneity in hardness, it is worth performing a final aging.

Electron Beam Cold Hearth Melted Titanium Alloys and the Possibility of Their Use as Anti-Ballistic Materials

Three commercial titanium alloys: two-phase α+β Ti-6Al-4V (low alloyed), and T110 (Ti-5.5Al-1.5V-1.5Mo-4Nb-0.5Fe, higher-alloyed), and β-metastable Ti-1.5Al-6.8Mo-4.5Fe were melted using EBCHM approach in the form of 100 mm in diameter ingots with the weight of about 20 kg each. After 3D hot pressing at single β-field temperatures ingots were rolled at temperatures below β-transus onto plates with thickness varying from 3 mm to 25 mm. Different heat treatments, including annealing at α+β or β-field temperatures, and special strengthening Surface Rapid Heat Treatment (SRHT) which after final aging provided special gradient microstructure with a hardened surface layer over ductile basic core, were employed. Mechanical properties were studied with tensile and 3-point flexure tests. It was established that the best combination of tensile strength and ductility in all alloys studied was obtained after SRHT, whereas at 3-point flexure better characteristics were obtained for the materials annealed at temperatures of (α+β)-field. At the same time, ballistic tests made at a certified laboratory with different kinds of ammunition showed essential superiority of plates having upper layers strengthened with SRHT. The effect of microstructure of the alloys, plate thickness and type of used ammunition on ballistic resistance is discussed.

Phase transformations and properties of concentration-inhomogeneous magnetic materials based on the Fe–30%Cr–27%Co system

The phase and structural transformations of a powder magnetically hard alloy of the system Fe–30%Cr–27%Co–1%Si–0,07%B with a metastable α1+α2 phase composition, a high content of cobalt, and a high level of magnetic properties were studied. The density and coefficient of variation of the concentration of the main elements of the sintered blanks at the level of deformable analogs are achieved by sintering in the α-phase with contact melting in the presence of a «vanishing» liquid phase formed due to the addition of silicon and boron ferroalloys. A kinetic approach to the development of a competitive hard magnetic alloy with a high proportion of the strongly magnetic phase is proposed. The effect of boron additions on the incubation period of the formation of an undesirable σ-phase and the temperature range of the concentration stratification of the α-solid solution on the strongly magnetic α1-phase and the weakly magnetic α2-phase were established. Optical microscopy, X-ray phase analysis and differential scanning calorimetry were used to determine temperature and time parameters of heat treatment of the alloy, including hardening, thermomagnetic treatment (TMT) and final aging, providing the required combination of Hc and Br by increasing the stability of the metastable α-phase up to 20 minutes in the interval temperatures of spinodal decomposition α → α1 + α2. The greatest increase in magnetic properties after TMT, observed at the 1st and 2nd steps of final aging, is related to the decomposition of the α-solid solution and the formation of subgrain boundaries. Elements of the obtained structure are characterized by submicron and nanometric sizes, which correlate with the research results on deformable alloys based on the Fe – Cr – Co system. The anisotropic α1+α2-structural state achieved by thermomagnetic treatment provided an increase in the magnetic properties of the studied 30H27KSR powder alloy to 30 % and the squareness coefficient of the magnetic hysteresis loop equal to 0,82 .

Two-Step Aging Behaviour of Solution Treated A356 System Alloy

Al-7mass%Si-0.3mass%Mg alloy is widely applied to the automotive components, such as road wheel or suspension frame because of having higher ductility and corrosion resistance. Two-step aging behavior of solution treated Al-7mass%Si-0.3mass%Mg system alloy A356 cast into permanent mold and solution treated was investigated by micro-vickers hardness measurement, optical microscopy (OM) and transmission electron microscopy (TEM). The microstructure of as-cast state was consist of primary crystallized α-Al and secondary crystallized eutectic phases. Al-7mass%Si-0.3mass%Mg alloy after casting, the test specimens were heat treated for different pre-aging temperatures at 273K, 348K and 423K for various times after solution treatment at 813K for 36ks. After pre-aging treatment, the test specimens were heat treated for artificial aging at 523K for various times. The peak hardness increased almost the same value when the pre-aging temperature was 273K. On the other hands, positive effect of the final-aging was occurred after pre-aging at 348K and 423K with significantly increasing hardness in the under-aging region. The fine precipitates were observed in the specimen which was final aging at 523K after pre-aging at 348K and 423K.Such a positive effect is considered due to the influence of precipitated phase mainly such as clusters and /or G.P.zone.The present study aims to investigate the effect of pre-aged temperature on final-aged behavior in A356 system alloy.

Experimental Study on Asphalt Composite UV Absorption Anti-Aging Agent

In order to compound high performance asphalt UV absorption anti-aging agent, light screener, antioxidant, light stabilizer were used in experiment, ultraviolet rays aging equation of asphalt was established, was used to stand for final aging quantity of asphalt pavement, aging equation and were used to research the performance of UV absorption anti-aging agent in different compound mode, optimum composite system of asphalt composite UV absorption anti-aging agent was found, and compliance dosage of components in optimum composite system was research after then. The results of the study show that: The aging law of asphalt ultraviolet radiation aging follows the equation next, ; asphalt UV absorption anti-aging agent composed by 5% antioxidant and 1.5% light stabilizer have the best anti-aging performance to UV radiation.

Behavior of Hydrogen in Electrolytically Charged Aluminum

Investigation on the behavior of hydrogen is needed to spread the use of hydrogen fuel cell vehicles. Hydrogen microprint technique (HMPT) has been known as an effective method to investigate the hydrogen behavior by visualizing the microscopic location of hydrogen in relation to the microstructure. In the present study, the behavior of electrolitically charged hydrogen in 6061 and 7075 aluminum alloys with T6-temper has been investigated by means of HMPT. Both in the two alloys, hydrogen was detected on constituent particles and in the matrix. Total amount of detected hydrogen was markedly larger in 7075 than in 6061, although the distribution in depth direction far narrower and the fraction of hydrogen detected in the matrix with respect to that on the constituent was larger. These fact was presumed to be caused by the difference in the fine precipitates between the two alloy formed during final aging treatment.

The Study on Microstructure and Properties of a New Metastable Beta Titanium Alloy after Aging Treatment

New metastable beta titanium alloy Ti-4Al-2.7V-12Mo-10Nb-1Zr-0.2Cr was carried out in the arc melting vacuum furnace. The microstructure and mechanical properties of a new metastable beta titanium alloy Ti-4Al-2.7V-12Mo-10Nb-1Zr-0.2Cr were compared at different aging temperature and time. The growth mechanism of α phase is analysed by comparing the morphology of the precipitated phase at different temperature. Test results indicate that titanium alloy Ti-4Al-2.7V-12Mo-10Nb-1Zr-0.2Cr has the best property through two-step aging treatment. The tensile strength of titanium alloy Ti-4Al-2.7V-12Mo-10Nb-1Zr-0.2Cr after final aging treatment achieves 1180MPa with 8% elongation trough tensile test. The strengthing mechanism was also discussed in this paper.

The Influence of Aging Process on Microstructures and Properties of an Al-2.54Li-1.61Cu-1.23Mg-0.22Zr Alloy

The influence of aging process on microstructures and mechanical properties of a rapid solidification Aluminum-Lithium alloy has been analyzed in this paper. The results show that the better aging process is as follows: heating to 170oC for 4 hours and then followed by a final aging at about 190 oC for 18 hours. A lot of fine participated second phase such as δ′ in matrix and a narrow participation free band make alloy’s good performance.

Nonlinear ultrasonic assessment of precipitation hardening in ASTM A710 steel

We investigated several specimens of ASTM A710 steel containing copper-rich precipitates with variations in the final aging treatment. X-ray diffraction line-broadening and small-angle neutron-scattering experiments revealed the existence of the precipitates and associated coherency strain. We determined the nonlinear ultrasonic parameter β for each specimen by harmonic-generation experiments and measured the ultrasonic longitudinal velocity vL and attenuation αL. Although vL and aL showed no consistent trends, β increased with increasing strain. This correlation is compared to a microstructural model for harmonic generation that includes a contribution from precipitate-inned dislocations.