Four new orientation relationships of Mg_(17)Al_(12) phase with magnesium matrix in Mg-8Al-0.5Zn alloys

Although the non-basal precipitates, those not parallel to the basal plane, are more effective to block basal slip in Mg-Al alloys, the crystallographic orientation relationship(OR) between these precipitates and the α-Mg matrix has not been well established. In this work, the crystallography of the non-basal Mg_(17)Al_(12) precipitates in AZ80 alloy was systematically investigated by transmission electron microscopy(TEM). By tilting to a suitable electron beam direction, different kinds of non-basal precipitates were recognized in TEM, and the following four new ORs between the non-basal Mg_(17)Al_(12) precipitates and the matrix were revealed: ■, and ■.Furthermore, these ORs and their habit planes were explained using the edge-to-edge matching model. The findings in this work can provide some guidelines for designing the microstructure of Mg-Al alloys to enhance their precipitation hardening potential.

Microstructure evolution,mechanical properties and tailoring of coefficient of thermal expansion for Cu/Mo/Cu clad sheets fabricated by hot rolling

The law of microstructure evolution and mechanical properties of hot roll bonded Cu/Mo/Cu clad sheets were systematically investigated and the theoretical prediction model of the coefficient of thermal expansion(CTE)of Cu/Mo/Cu clad sheets was established successfully.The results show that the deformation of Cu and Mo layers was gradually coherent with an increase in rolling reduction and temperature and excellent interface bonding was achieved under the condition of a large rolling reduction.The development of the microstructure and texture through the thickness of Cu and Mo layers was inhomogeneous.This phenomenon can be attributed to the friction between the roller and sheet surface and the uncoordinated deformation between Cu and Mo.The tensile strength of the clad sheets increased with increasing rolling reduction and the elongation was gradually decreased.The CTE of Cu/Mo/Cu clad sheets was related to the volume fraction of Mo.The finite element method can simulate the deformation and stress distribution during the thermal expansion process.The simulation result indicates that the terminal face of the clad sheets was sunken inward.

Evaluation of the reliability of twin variant analysis in Mg alloys by in situ EBSD technique

Electron backscatter diffraction(EBSD)is an orientation mapping technique,which has been widely used to study texture evolution and twinning behavior.This work aims to study the variant of{10¯12}twins during tensile deformation of AZ31 Mg alloys.An in-situ tensile stage was used,and coupled with EBSD technique,the variants of twins can be analyzed without releasing the tensile stress.Based on the EBSD maps,the first and second smallest misorientation angles(M_(1)and M 2)between each active twin and respective potential variants were calculated,and the distribution of M_(1)values with tensile strain was obtained.The results indicated that{10¯12}twins were deviated from their ideal orientations with strain increased.The criteria of M_(1)<4°and M 2−M_(1)>2°were suggested to be applied to select the data points for reliable variant identification.Moreover,it confirmed that the deviation of twin relationship was ascribed to the profuse basal glide in matrices and/or twins.

Fine-grained Mg−1Mn−0.5Al−0.5Ca−0.5Zn alloy with high strength and good ductility fabricated by conventional extrusion

Mg−1Mn−0.5Al−0.5Ca−0.5Zn(wt.%)alloy was fabricated by conventional extrusion at 673 K with an extrusion ratio of 25:1,followed by aging at 473 K.The microstructure was characterized by scanning electron microscopy,electron back-scattered diffraction,and transmission electron microscopy.The mechanical properties were determined by the tensile test.The peak-aged sample shows fine recrystallized grains with an average grain size of 1.7μm.Area fraction of Al−Ca particles in the alloy increases significantly after peak aging.Meanwhile,botháañandác+añdislocations were observed to remain in the alloy after hot extrusion.Thus,the peak-aged sample exhibits simultaneously high strength and good ductility with the ultimate tensile stress,tensile yield stress,and tension fracture elongation of 320 MPa,314 MPa,and 19.0%,respectively.

Influence of texture distribution in magnesium welds on their non-uniform mechanical behavior:A CPFEM study

Recent studies indicate that the texture distribution in friction stir welded(FSW)Mg alloys can be tailored and hence improve the joint performance.In this work,a crystal plasticity finite element modeling(CPFEM)was performed to understand the effects of texture distribution in stir zone(SZ)on the nonuniform plastic deformation and fracture localization.In total,six kinds of observed or purposely tilted texture distributions were modelled.The"concave-convex"appearance,as commonly observed in the tensile sample,was successfully simulated.It reveals that the mirror-symmetrical distribution of basal planes in the region of easy to activate basal slip(EABS)determined the"concave-convex"appearance in SZ-center.The asymmetrical appearance exchanged on plane A and plane B when the directions of basal planes were switched in the two EABS regions.Furthermore,the asymmetrical feature of plastic deformation was changed with varying the texture distribution in SZ.The"embossed"feature became more obvious in SZ-center first,and then gradually weakened with the c-axis rotated away from the weld plate plane.Severe necking was successfully simulated in SZ-center of FSW-H joint and in SZ-side of FSW-L joint.That might determine the observed fracture morphology.We believe that this simulation study is helpful for further improving the performance of FSW Mg joints.

Effect of lamellar structural parameters on the bending fracture behavior of AA1100/AA7075 laminated metal composites

The lamellar structure has an important impact on the mechanical properties of dissimilar laminated metal composites(LMCs),including the thickness ratio of dissimilar metal constituent layers and the number of layers.AA1100 and AA7075 with thickness ratios of 1:4 and 3:4 were fabricated for multilayer AA1100/AA7075 LMCs by hot accumulative roll bonding(ARB)technology.The bending fracture characteristics of AA1100/AA7075 LMCs with different thickness ratios and numbers of constituent layers were investigated.The research results indicated that AA1100/AA7075 LMCs with a low thickness ratio exhibited better bending ductility and toughness than those with a high thickness ratio,which was attributed to the crack growth resistance caused by the thickness of the soft AA1100 layer.The toughening mechanism introduced by crack deflection or arresting contributed to the enhancement in the toughness of the LMCs compared with that of the single 7075 Al layer.The bonding interfaces of AA1100/AA7075 LMCs with different numbers of layers are continuous and straight due to the high ARB temperature.A decrease in bending toughness was observed as the number of layers increased.Unlike LMCs with a low number of layers,crack deflection or interface delamination is also considered a main toughening mechanism in dissimilar LMCs in addition to the thickness effect.