Effect of vibration on interfacial microstructure and mechanical properties of Mg/Al bimetal prepared by a novel compound casting

In this work,a vibration was applied in the preparation of the Mg/Al bimetal by a novel compound casting in order to improve the mechanical properties of the Mg/Al bimetal,and the effect of the vibration on the interfacial microstructure and mechanical properties of the Mg/Al bimetal was investigated.The results indicated that the vibration had a significant effect on the interfacial microstructure and mechanical properties of the Mg/Al bimetal,but it did not change the phase compositions of the interface,which was composed of layerⅠ(Al3Mg2+Mg2Si),layerⅡ(Al_(12)Mg_(17)+Mg_(2)Si)and layerⅢ(Al_(12)Mg_(17)/δ-Mg).Without vibration,the Mg_(2)Si phase with a needle-like morphology mainly aggregated in the layerⅡof the interface.After the application of the vibration,the SEM and EBSD analysis results showed that the Mg_(2)Si and Al3Mg2phases in the interface were obviously refined,and the distribution of the Mg_(2)Si became more uniform,due to the strong forced convection of the molten metal resulting from the vibration.The TEM analysis indicated that the interface between the A_(l3)Mg_(2) and Mg_(2)Si phases was non-coherent,suggesting the Mg_(2)Si particles cannot act as a heterogeneous nucleation base during the solidification process of the interface.Compared to the Mg/Al bimetal without vibration,the shear strength of the Mg/Al bimetal with vibration increased by about 50%from 31.7 MPa on average to 47.5 MPa,and the hardness of the layer I of the interface increased,and the hardness of the layerⅢdecreased.The fracture surface transformed from a flat fracture morphology without vibration to an irregular zigzag fracture morphology.

Effect of La on microstructure,mechanical properties and fracture behavior of Al/Mg bimetallic interface manufactured by compound casting

To improve the Al/Mg bimetallic interface,La was added into the Al/Mg bimetallic interface manufactured by a compound casting process.The effect of La addition on the microstructure,mechanical properties and fracture behavior of the Al/Mg bimetallic interface and the formation mechanism of the interface were studied in detail.Al_(11)La_(3),Al_(8)Mn_(4)La,Al_(20)Ti_(2)La,and other rare earth precipitates(RE precipitates)preferentially precipitated at the interface with La addition,while the number of the Al_(11)La_(3)and Al_(8)Mn_(4)La located in eutectic structure area(E area)gradually increased and aggregated in the interface with the increase of the La content.Besides,the matrix structure in different areas of the Al/Mg interface changed in different degrees,and the eutectic structure and primaryγ(Mg_(17)Al_(12))dendrites in the E area were refned,but the intermetallic compounds area(IMC area)had no obvious change.With the addition of the La,the interface was strengthened under the comprehensive effect of refnement strengthening and precipitation strengthening from the E area.When the La content increased to 1.0%,the shear strength of the Al/Mg bimetal reached the maximum of 51.54 MPa,which was 30.95%higher than the group without La addition.However,with the further increase of the La content,the large area aggregation of the Al_(11)La_(3)and Al_(8)Mn_(4)La occurred in the interface,leading to the separation of the matrix structure of the E area and the decrease of the shear strength of the Al/Mg interface.