Effects of aging on the microstructures and mechanical properties of extruded AM50+xCa magnesium alloys

The effects of aging treatment on the microstructures and mechanical properties of extruded AM50 ＋ xCa alloys （x=0, 1, 2 wt.%） were studied. The results indicated the secondary phase Mgl7Al12 precipitated from the saturated α-Mg solid solution while Al2Ca changed slightly when the aging time was increased. The hardness of extruded AM50 ＋ xCa al- loys increased initially to its peak, and then dropped to reach its original hardness with the increase in aging time. With the increase in aging temperature, the hardness of the AM50 ＋ 2Ca ahoy decreased, whereas the hardness of AM50 and AM50 ＋ 1Ca alloys decreased in the initial stages of aging treatment and increased in the later stages of aging treatment. The tensile strengths of AM50 and AM50 ＋ 1Ca alloys increased after aging treatment for the precipitation of Mg17Al12 phase, which increases the resistance against dislocation movement at the grain boundary; with increase in aging temperature, their tensile strengths increased. For AM50 ＋ 2Ca alloy, the tensile strength declined after aging at 150℃ and 175℃, while it increased slightly at 200℃. The ductility of AM50 ＋ xCa alloys （x = 0, 1, 2 wt.%） declined after aging treatment.

Effects of aging on the microstructures and mechanical properties of extruded AM50+xCa magnesium alloys

The effects of aging treatment on the microstructures and mechanical properties of extruded AM50+xCa alloys （x=0,1%,2% in mass fraction） were studied. The results indicated the secondary phase Mg 17 Al 12 precipitated from the saturated α-Mg solid solution while Al2Ca changed slightly when the aging time was increased. The hardness of extruded AM50+xCa alloys increased initially to its peak,and then dropped to reach its original hardness with the increase in aging time. With the increase in aging temperature,the hardness of the AM50+2Ca alloy decreased,whereas the hardness of AM50 and AM50+1Ca alloys decreased in the initial stages of aging treatment and increased in the later stages of aging treatment. The tensile strengths of AM50 and AM50+1Ca alloys increased after aging treatment for the precipitation of Mg 17 Al 12 phase,which increases the resistance against dislocation movement at the grain boundary; with increase in aging temperature,their tensile strengths increased. For AM50+2Ca alloy,the tensile strength declined after aging at 150?℃ and 175?℃,while it increased slightly at 200?℃. The ductility of AM50+xCa alloys （x=0,1%,2%） declined after aging treatment.

Microstructure and mechanical properties of NZ30K alloy by semi-continuous direct chill and sand mould casting processes

The Mg-3.0Nd-0.2Zn-0.4Zr (NZ30K) alloys were prepared by direct-chill casting (DCC) and sand mould casting (SMC) processes,respectively and their microstructures and mechanical properties were investigated.The results indicate that casting method plays a remarkable influence on the microstructure and mechanical properties of as-cast NZ30K alloy.The grain size increases from 35-40μm in the billets made by the DCC to about 100-120μm in the billets by the SMC.The aggregation of Mg12Nd usually found at the triple joints of grain boundaries in the billets prepared by SMC while is not observable from the billets by DCC.The tensile strengths and elongations of the billets are 195.2 MPa and 15.5% by DCC,and 162.5 MPa and 3.2% by SMC,respectively.The tensile strength of the alloy by DCC is remarkably enhanced by T6 heat treatment,which reached 308.5 MPa.Fracture surfaces of NZ30K alloy have been characterized as intergranular fracture by SMC and quasi-cleavage fracture by DCC,respectively.

Microstructure and mechanical properties of rolled Mg-12Gd-3Y-0.4Zr alloy sheets

The extruded Mg-12Gd-3Y-0.4Zr alloy sheets were rolled from 30 mm to 2.3 mm at 723 K by electric heated rollers,and then different heat treatments were performed to improve their properties.The microstructures and tensile properties of the alloy sheets were investigated,including as-rolled,annealed and T5 treated.The experimental results show that the grains are effectively refined by the rolling process,and the strength of the rolled alloy is greatly enhanced.The annealed alloy exhibits lower strength and higher elongation than the rolled one,while the aged alloy shows higher strength and lower elongation.After being aged at 498 K for 17 h,the alloys get the highest strength,namely,the ultimate tensile strength is 456.8 MPa,yield strength is 348.9 MPa,and elongation is 3.8%.

Effectively refining Al-10Si alloy via Al-Ti-Nb-B refiner with Nb_(2)O_(5)

Al-Si alloys have excellent corrosion resistance,low thermal expansion coefficient,and high strength-to-weight ratio,which make them widely used in structural components in the automotive and aerospace industries[1,2].However,the coarseα-Al dendrites result in poor mechanical properties[3,4],and the widely used Al-5Ti-B(all compositions are in wt.%unless otherwise specified)refiner fails in as-cast aluminum alloys with high silicon content(≥5 wt.%)due to the Si-poisoning effect[5,6].Fortunately,in order to overcome Si-poisoning,a series of refiners have been developed.Al-B refiner is effective for refining aluminum alloys with high silicon content,but it is easy to be poisoned by Ti/Zr[7,8].Al-Nb-B[9–11]and Al-V-B[12]refiners have a certain ability to overcome Si-poisoning,while the nucleating particles have a large density and are easy to agglomerate and settle,leading to the grain refinement fading phenomenon.Al-Ti-C-B refiner realizes the anti-Si/Zrpoisoning ofα-Al grain refinement based on the evolving effect of a doped TCB complex[13,14].Al-Ti-Nb-B refiner prepared with Nb partially substituted Ti can improve the refinement level of Al-10Si alloy to 109–125μm[15,16].However,the existing preparation method of the refiner uses pure Nb powder as raw material,resulting in high preparation costs,which limits its application in industry to a certain extent.

Achieving ultra-high strength in Mg-Gd-Ag-Zr wrought alloy via bimodal-grained structure and enhanced precipitation

Mg-13.1 Gd-1.6 Ag-0.4 Zr(wt%)alloy was either iso-thermally extruded at 350℃ or differentialthermally extruded with respectively pre-heated billet at 500℃ and die at 350℃.The iso-thermal extrusion leads to a near fully recrystallized structure and a[0001]//ED(extrusion direction)texture.In contrast,the differential-thermally extruded alloy develops a bimodal-grained structure composed of fine equiaxed recrystallized grains and coarse elongated unrecrystallized grains with a0110//ED texture.The differential-thermally extruded alloy has a higher number density of precipitates after postextrusion ageing than that of the iso-thermally extruded counterpart.Moreover,precipitation in the differential-thermally extruded alloy is further enhanced with cold rolling before ageing.Finally,the alloy obtains room temperature tensile yield strength of 421 MPa and ultimate tensile strength of 515 MPa via differential-thermal extrusion,cold rolling and ageing,mainly ascribed to the coupled strengthening from the bimodal-grained structure and enhanced precipitation.Strength of the alloy is noticeably higher than those of Mg-Gd(-Y)-Ag extruded alloys with similar compositions reported previously and is comparable to those of other high-strength Mg wrought alloys.The findings suggest that differentialthermal extrusion plus strain ageing is a suitable approach for achieving high strength in age-hardenable Mg alloys.