Search results

A 3D finite element (FE) model based on the double ellipsoidal heat source was developed to investigate the evolution of temperature and stress fields during the multilayer and multi-pass wire and arc additive manufacturing (WAAM) process. This paper aims to investigate the evolution of temperature and stress fields during the multilayer and multi-pass wire and arc additive manufacturing (WAAM) process by developing a 3D finite element (FE) model based on the double ellipsoidal heat source.

Experimental thermal cycle curves and residual stresses were obtained by thermocouples and X-ray diffraction, respectively. The validity of the model was verified by the corresponding experimental results.

The deposition process of the upper pass led to the partial remelting of the lower deposited pass. The thermal process of the current-deposited pass alleviated the stress concentration in the previous-formed passes. A more uniform temperature distribution could be obtained by using the reciprocating deposition path. Compared to the reciprocating deposition path, the peak values of the transverse and longitudinal tensile residual stresses of the deposited sample under the unidirectional deposition path were reduced by 15 MPa and increased by 13 MPa, respectively. The heat conduction in the deposited passes could be improved by extending the inter-pass cooling time appropriately. With an increase in the inter-pass cooling time, the longitudinal residual stress in the middle region of sample along longitudinal and transverse directions showed increase and decrease–increase trends, respectively, while the transverse residual stress exhibited decrease trend.

This study enhances the understanding of temperature and stress fields evolution during the multilayer and multi-pass cold metal transfer-WAAM processes of magnesium alloy and provides the reference for parameter optimization.

Effects of major factors, such as alloy composition, crystal structure and grain size, on mechanical properties of TiZr based alloys are investigated and summarized in this work. The microhardness of TC4 alloy obviously increases 15.3% and 17.6% after 30 wt.% and 47 wt.% Zr additions, respectively. Nanoindentation results show that the average nanoindentation hardness of α phase in annealed 30 Zr is approximately 18% higher than that of retained β phase. Tensile test results show that variation in strength of basketweave microstructural 30 Zr alloy with original β grain size from 100 to 203 μm is less than 2%.

The Zr-40Ti-4.5Al-4.2V (ZT40) alloy is one of new developed Zirconium alloys with high mechanical properties and great potential for application. The investigation about effects of plastic deformation on microstructure and mechanical properties can promote practical applications of the new high performance ZrTi based alloys. The microstructural evolution and mechanical properties of the ZT40 alloy suffered hot rolling with thickness reduction from 30% to 60% at 775 °C are investigated in this work. Results show that the phase constitution changes from (α + β) to (β + fcc) while the original specimen underwent hot rolling and subsequent water quenching. The β phase in hot rolled specimen adopts preferred orientation form (200) and (211) planes to only (200) plane while the rolling reduction increases from 30% to 60%. Furthermore, no obvious preferred orientation can be detected in specimen with reductions of 60%. Micrographs analysis shows that the dynamic recrystallization occurs in hot rolled specimens. Volume fraction of the DRX grains is approximately 8% in 30% reduction specimen and increases with the increasing of rolling reduction. Nearly full recrystallization is observed in the specimen with reductions of 60%. Hardness test shows that the HV of hot rolled specimen decreases from 384 HV to 329 HV as the increasing of reduction from 30% to 60%. The mechanisms of microstructural evolution and variation of hardness are also discussed. The finding should contribute to understand microstructural evolution, to adjust mechanical properties and to promote practical applications of Zirconium alloys.