حساسیت به ترک انجمادی در فلزهای جوش آلیاژهای آلومینیوم

Solidification crack susceptibility of aluminum alloy weld metals 

حساسیت به ترک انجمادی در فلزهای جوش آلیاژهای آلومینیوم

ABSTRACT

The susceptibilities of the three aluminum alloys to solidification crack were studied with trans-varestraint tests and tensile tests at elevated temperature. Their metallurgical characteristics, morphologies of the fractured surface and dynamic cracking behaviors at elevated temperature were analyzed with a series of micro-analysis methods. The results show that dynamic cracking models can be classified into three types. The first model has the healing effect which is called type A. The second is the one with deformation and breaking down of metal bridge, called type B. The last one is with the separation of liquid film along grain boundary, called type C. Moreover, the strain rate has different effects on crack susceptibility of aluminum alloys with different cracking models. ZL101 and 5083 alloys belong to type A and type C cracking model respectively, in which strain rate has greater effect on eutectic healing and plastic deformation of metal bridge. 6082 alloy is type B cracking model in which the strain rate has little effect on the deformation ability of the liquid film.

 

روند پیشرفت نظریه انجماد غیر تعادلی

Progress of Nonequilibrium Solidification Theory

روند پیشرفت نظریه انجماد غیر تعادلی

ABSTRACT

This paper summarized the theory related to nucleation, interface kinetics, micromorphology evolution and microscopic growth during nonequilibrium alloy solidification. Methods for quantitative analysis of nucleation rate, the criterion of marginal stability, nonequilibrium partition coefficient, as well as the relationship between growth rate with undercooling and dendrite tip radius are presented. Some limitations and future developments of nonequilibrium theory are pointed out.

 

اثر میدان مغناطیسی عرضی بر رشد دانه های هم محور حین انجماد جهت دار

Effect of a transverse magnetic field on the growth

of equiaxed grains during directional solidification

اثر میدان مغناطیسی عرضی بر رشد دانه های هم محور حین انجماد جهت دار

ABSTRACT

The effect of a transverse magnetic field on the growth of equiaxed grains during directional solidification of Al-10wt% Cu alloys was investigated experimentally and numerically. The experimental results show that the magnetic field has a great influence on the size and distribution of equiaxed grains. Indeed, the magnetic field causes refined and coarsen equiaxed grains to distribute on the both sides of the sample, respectively. In-situ synchrotron X-ray imaging shows that a transverse magnetic field induced some force which can act on equiaxed grains and cause the movement of equiaxed grains during directional solidification. Numerical results reveal that the modification of the structure may be attributed to the thermoelectric (TE) magnetic effects produced by the magnetic field. Furthermore, a new method of removing inclusions in molten metal is developed by means of the TE magnetic force.

 

حرکت دانه های هم محور در حین انجماد جهت دار تحت میدان مغناطیسی استاتیک

Motion of equiaxed grains during directional solidification

under static magnetic field

حرکت دانه های هم محور در حین انجماد جهت دار تحت میدان مغناطیسی استاتیک

ABSTRACT

The in situ and real time observations of the equiaxed grain motion during directional solidification of Al–10 wt% Cu under static magnetic field has been carried out by means of synchrotron X-ray radiography. It was observed that equiaxed grains moved approximately along the direction perpendicular to both the imposed magnetic field and the temperature gradient. Based on the radiographs, the motion of the solid grains was analyzed for various temperature gradients, and it was shown that the trajectories were imposed by the combination of the Thermo-Electric Magnetic forces, induced by the coupling of thermo-electric currents with the permanent magnetic field and the gravity force. The variations of the velocities and sizes of grains during the equiaxed growth under static magnetic field were measured and compared to a simple analytical model for the Thermo-Electric Magnetic forces and the Stokes law. A good agreement was achieved for the deviation angle as a function of the grain diameter, while a large discrepancy was observed for the velocity intensity when the dimensions of the equiaxed grains increased. In the latter case, it was shown that the corrections for both sample confinement and grain morphology were mandatory to explain the very low values of grain velocities.

 

تاثیر انجماد بر تحول ریزساختاری فلز جوش پایه نیکل

Influence of solidification on the microstructural evolution

of nickel base weld metal

تاثیر انجماد بر تحول ریزساختاری فلز جوش پایه نیکل 

ABSTRACT

The effect of segregation resulting from solidification on the microstructural evolution of nickel base alloys was investigated. Two different groups of alloys were produced to simulate either the Hastelloy C type or the Inconel 625/718 type of alloys. Gravitational thermal analysis welding was performed on these experimental alloys and the extent of microsegregation in the weld metal was determined. Using composition profiles obtained from solidified microstructures, predictions of the phase stability of these microstructures were made based on metal d-level (Md) calculations. The maximum Md values obtained in these microstructures were compared with those critical to the formation of topologically close-packed (TCP) phases such as sigma, P, and Laves. These profiles showed an increase in the Md level in the interdendritic regions which was correlated to the formation of TCP phases.