Effect of grain refinements on the microstructure and thermal behaviour of Mg–Li–Al alloy

Abstract

The light as-cast Mg-9Li-1.5Al alloys were manufactured and modified by 0.2 mass% Zr, commercial 0.2 mass% TiBor and 0.2 mass% AlSr master alloys. The thermal derivative analysis using UMSA platform was utilised to characterise a crystallisation process. Samples were heated up to 700°C and then freely cooled down (* 0.6°C s-1) to ambient temperature in order to simulate the natural cooling of casts. Dilatometry study was used to identify changes in solid state. The relative elongation of unmodified and modified alloys was measured in the temperature range from 20 to 400°C, with a heating rate 1.0°C s-1. The effects of Zr, TiBor and AlSr content on the microstructure of analysed magnesium alloys were investigated. Evaluation of microstructure was identified by light microscope, scanning electron microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy. The results showed that the addition of TiBor reduced the grain size of Mg-9Li-1.5Al cast alloy from 930 to 530 lm, while the addition of AlSr master alloy reduced the grain size to 480 lm. Moreover, an addition of TiBor and AlSr simultaneously reduced the grain size to 430 lm. The addition of Zr causes a reduction in grain size to 630 lm. The addition of grain refinement causes changes in crystallisation process and variations in the coefficient of linear thermal expansion (CTE).

Magnesium–lithium alloys with TiB and Sr additions

“…Variation of hardness of as-cast alloys with the addition of TiB and Sr grain modifiers metastable intermetallic phase g(LiAl) with B2 structure [16][17][18]. 4-T g(LiAl) -nucleation of g(LiAl) phase is observed at 554.49°C (Mg-4.5Li-1.5Al ?…”

The Effect of Long-Term Ageing on the Degradation of the Microstructure the Inconel 740h Alloy

“…For materials used in the construction of steam boilers, the requirement is only adequate creep strength but also high mechanical properties, both at room and elevated temperatures. The process of changes in the functional properties of these materials, and thus changes in their microstructure, describe the material characteristics that, in connection with the methods of assessing their exhaustion, are used to allow them to continue to work safely in both computational and off-set working hours [21][22][23][24][25][26].…”

The phase transitions in selective laser-melted 18-NI (300-grade) maraging steel

“…The transitions kinetics of the reaction in solid state in a component may be diagnosed by quantifying the variation in physical properties such as hardness, dilation, electrical resistivity or enthalpy as a function of reaction temperature and time. One of the methods that provide precise information about transitions in solid state during heating and cooling cycles is dilatometry [16][17][18][19][20][21][22][23]. This technique is a very sensitive and appropriate method for examining phase transformations, which revealed its strengths on measurements of a wide range of steels, such as maraging steels and lowcarbon steels.…”

“…Common applications embrace thermal expansion, annealing studies, determination of phase transformations and the glass transition, softening points, kinetics studies, development of phase diagrams, including the determination of sintering temperature, sintering step and rate-controlled sintering. The phase transitions taking place in the continuous cooling process or the isothermal plateau is indicated by the determined difference of length [14,15,18,19,[22][23][24][25].…”