Effect of age-forming on microstructure, mechanical and corrosion properties of a novel Al–Li alloy

In the present work, effects of creep ageing (CA) on the mechanical properties and micro precipitates of Al-Li-S4 alloy was investigated. Compared with single stress-free ageing (SFA), experimental results show that CA has significantly improved the mechanical properties of Al-Li-S4 alloy, including hardness, strength and elongation. Meanwhile, the peak-ageing time was also prolonged under CA treatment. When specimens were continuously placed under an exterior stress of 240 MPa after CA treatment at 153 °C for 25 h, more T 1 (Al 2 CuLi) nano-precipitates developed and further contributed improvement in mechanical properties. It is mainly attributed to the exterior stress that promoted to form T 1 nano-precipitates. Moreover, CA enabled to restrict both the coarsening of precipitates at grain boundaries and the formation of precipitation free zone. In addition, fractographic examination of SFA-treated and CA-treated Al-Li-S4 tensile specimens were carried out, respectively. Through controlling the formation process of fine T 1 nano-precipitates during CA treatment, it can facilitate the development of novel microstructures in Al-Li-S4 alloys with certain promising mechanical properties.

Effects of uniaxial creep ageing on the mechanical properties and micro precipitates of Al-Li-S4 alloy

Quantification of the detrimental effects of precipitate free zones on the yield strength of a superalloy

We have examined spheroidization and coarsening of cementite in an initially pearlitic 2C-4Cr ultrahigh carbon steel containing a cementite network. Coarsening kinetics of spheroidized cementite and growth of denuded zones adjacent to the cementite network were investigated by analyzing particle sizes from digital micrographs of water-quenched steel etched with Nital. Denuded zones grew at a rate proportional to t
 1/4–t
 1/5. Spheroidization of pearlite was completed within 90 minutes at 1073 K and 1173 K (800 °C and 900 °C), and within 5 minutes at 1243 K (970 °C). Bimodal particle size distributions were identified in most of the samples and were more pronounced at higher temperatures and hold times. Peaks in the distributions were attributed to the coarsening of intragranular and grain boundary particles at different rates. A third, non-coarsening peak of particles was present at 1073 K (800 °C) only and was attributed to particles existing prior to the heat treatment. Particle sizes were plotted vs time to investigate possible coarsening mechanisms. The coarsening exponent for the growth of grain boundary carbides was closest to 4, indicating grain boundary diffusion control. The coarsening exponent was closest to 5 for intragranular carbides, indicating suppression of volumetric diffusion (possibly due to reduced effective diffusivity because of Cr alloying) and control by dislocation diffusion.

Coarsening of Inter- and Intra-granular Proeutectoid Cementite in an Initially Pearlitic 2C-4Cr Ultrahigh Carbon Steel

The application of electropulsing treatment (EPT) is studied on the microstructure and hardness of cold-rolled low carbon steel. The effects of electrical pulses on the grain refinement, precipitate size evolution and hardness are investigated. It is found that applying electrical pulse decreases the grain and precipitate size and increases the hardness in the early stages of electropulsing, but the grain and precipitate size is increased and the hardness is decreased by continuing electropulsing. Also, the effect of electropulsing treatment variables as well as treated time and number of periods are discussed. It is demonstrated that increasing treated time can accelerate achieving maximum hardness in lower number of periods.

D.P. Yao

Papers

The formation and growth of PFZ at grain boundary in Al-11.9at.-%Li alloy

The permeability of hydrogen in 18Ni maraging steel