Mg-2nd-0.2zn-0.4zr-xy Magnesium Alloy Microstructure And Mechanical Properties

The influences of uniform treatment, aging treatment and solution treatment on the microstructures and mechanical properties of as cast Mg-2Nd-0.2Zn-0.4Zr-xY alloys were investigated by optical microscope, X-Ray diffraction (XRD), scanning electron microscope (SEM containing energy spectrum analysis), transmission electron microscope (TEM), hardness test and tensile test methods. The following conclusions were drawn as follows:(1) The grain of as-cast Mg-Nd-Zn-Zr alloys was greatly refined by the addition of Y element, especially with the addition of 6wt.%Y, which mechanical property have the best synthetical properties that the ultimate tensile and ultimate tensile stress are 233MPa,150MPa respectively, and the elongation was 16%. The mainly composed of as-cast Mg-2wt.%Nd-0.2wt.%Zn-0.4wt.%Zr alloy without addition of Y is Mg12Nd, whereas, the element Nd and Y exist as Mg41Nd5 and Mg24Y5 in alloys containing Y.(2) Reticular Mg12Nd compounds in Mg-2Nd-0.2Zn-0.4Zr alloy was dissolved after solution treatment at 525℃for 14 h, and the alloy was mainly composed of a-Mg matrix and some unknown strip-shipped compounds which contained Zn, Zr and Mg. Mg41Nd5 compounds which alonged grain boundaries in Mg-2Nd-0.2Zn-0.4Zr-xY alloys were dissolved and disappeared after solution treatment at 515℃for 8h, and the alloys were mainly composed of a-Mg matrix, cubic Mg2Y compounds, lightly remained cubic Mg24Y5 compounds and strip-shipped and some unknown strip-shipped phase which contained Zn, Zr and Mg.(3) The suitable heat treatment of Mg-2Nd-0.2Zn-0.4Zr alloy was optimized to be 525℃×14 h+200℃×10 h. Metastableβ″phase is the dominating precipitated in the peak-aged alloy. The suitable solution treatment of Mg-2Nd-0.2Zn-0.4Zr-xY(x=4,6,8) alloys were optimized to be 515℃×8 h, while the aging treatment varied to be 220℃×20 h,220℃×10 h,220℃×10 h with the volume of Y ranging from 4 %to 6%respectively. Theβ′phase is dominating precipitated in these peak-aged alloys, whereas the plate-like stableβphase which distribute along three orientations exist in the over-aged alloys.(4) Strengths of the peak-aged Mg-2Nd-0.2Zn-0.4Zr-xY(x=4,6,8) alloys increased in a large scale compared with the alloy free of Y. And Mg-2Nd-0.2Zn-0.4Zr-6Y alloy exhibited the best mechanical property of 269 MPa in ultimate tensile stress,187 MPa in yield tensile stress and 7.6% in elongation to failure.