Morphology evolution of Al_9(Mn, Ni)_2 eutectic phase in Al-4Ni-2Mn alloy during heat treatment at 350℃

The morphology evolution of AI9（Mn,Ni）2 eutectic phase in AI-4Ni-2Mn alloy at 350 .C was examined. Two kinds of morphology evolution trends of AIg（Mn, Ni）2 eutectic phase were observed by using scanning electron microscopy and transmission electron microscopy. The ribbon-like AIg（Mn, Ni）2 eutectic phase taking up a small portion of the eutectic structures gradually changes from ribbon-like morphology to rod-like during the heat treatment. The rod-like AIg（Mn, Ni）2 eutectics, primary eutectic structure in the alloy, become unstable at the transverse sub- boundaries of the eutectic rod when the samples are heat treated at 350 .C, and then split up into short rods with the extension of heat treatment time. Also, the Vickers microhardness test was used to characterize the change of local mechanical properties. The hardness test results indicate that local morphology evolution of eutectic phase has no obvious effect on the local mechanical properties of the alloy. The microhardness of the eutectic area increases slightly when the heat treatment time is extended to 192 h or 360 h.

Casting of aluminum-copper based alloy by controled difusion solidiication

A quaternary alloy （Al-5.0Cu-0.35Mn-0.25Ti, wt.%）, having a similar chemical component with ZL205A, was prepared using a controlled diffusion solidification （CDS） process and a conventional casting process. The effect of the casting process on microstructure and hardness was investigated. The grain morphology and casting defects of the al oy prepared via the conventional casting and CDS were observed and compared at various pouring temperatures. Results show that the CDS process can al eviate the hot tearing defects and reduce the density of porosity, while getting rid of the riser that is general y used for feeding during conventional casting. Structure observations show that the grain morphology of the conventional cast al oy is mainly dendritic, and the grain size decreases when the pouring temperature is decreased, while the CDS cast al oy consists of a large number of spherical grains, which can decrease the thermal cracking tendency and segregation defect, and enhance the hardness of the alloy.

Phase transformation behavior of Al_9(Mn,Ni)_2 eutectic phase during heat treatment at 600°C in Al-4Ni-2Mn alloy

The morphology evolution and phase transformation of Al9(Mn,Ni)2 eutectic phase in an Al-4Ni-2Mn alloy during heat treatment at 600°C were studied by scanning electron microscopy(SEM)and transmission electron microscopy(TEM).Results show that nearly all of the eutectic fibers change into prolate ellipsoid and spherical particles in the process of heat treatment,and Ostwald ripening phenomenon occurs in the eutectic region with the increase of the heat treatment time.Besides,a phase transformation from Al9(Mn,Ni)2 to O-phase is confirmed.The morphologies of the transformed particles indicate that the O-phase preferentially nucleates on the specific crystal plane of the Al9(Mn,Ni)2 eutectic phase and grows in a certain direction.During the phase transformation,the(010)[001]slip system in O-phase is activated,and the resultant slip traces appear on the surface of some O-phase particles.

Dual characteristic of trace rare earth elements in a commercial casting Al-Cu-X alloy

The effect of rare earth elements on microstructure and mechanical properties of casting Al-Cu-X alloy （X = Mn, Ti, V, Cd, Zr） was investigated in as-cast and T6 conditions. Microstructure evolution was characterized by optical microscopy, scanning electron microscopy, and transmission electron microscopy. RE-containing intermetallic compounds （IMCs） formed in this alloy were indentified by X-ray diffraction （XRD） and energy dispersive spectroscopy （EDS）. It is shown that the additions of RE （60Ce-40La, wt%） result in the formation of Ce-rich blocky-shaped A12o（Ti, V）2RE and La-rich skeletal-shaped A18Cu4RE. Tensile results of samples after T6 treatment indicate that the strength and ductility increase slightly to 480 MPa and 9.7 %, respectively, with RE content increasing from 0 wt% to 0.3 wt%. This is due to the combinative hardening effects of reduced grain size, enhanced precipitation of 0＇ （Al2Cu） phase and Al20 Cu2Mn3 dispersed particles, and minor La-rich IMCs at the grain boundaries of α-Al dendrites. The decrease of strength of 0.5 wt% RE-added sample is ascribed to the aggregation of Al20（Ti, V）2RE IMCs inside the grains. The dual characteristic of rare earth elements was also discussed in terms of its positive and negative effects on mechanical properties.