Dynamic recrystallization,texture and mechanical properties of high Mg content Al−Mg alloy deformed by high strain rate rolling

The Al−Mg alloy with high Mg addition(Al−9.2Mg−0.8Mn−0.2Zr-0.15Ti,in wt.%)was subjected to different passes(1,2 and 4)of high strain rate rolling(HSRR),with the total thickness reduction of 72%,the rolling temperature of 400℃and strain rate of 8.6 s^(−1).The microstructure evolution was studied by optical microscope(OM),scanning electron microscope(SEM),electron backscattered diffraction(EBSD)and transmission electron microscope(TEM).The alloy that undergoes 2 passes of HSRR exhibits an obvious bimodal grain structure,in which the average grain sizes of the fine dynamic recrystallization(DRX)grains and the coarse non-DRX regions are 6.4 and 47.7mm,respectively.The high strength((507±9)MPa)and the large ductility((24.9±1.3)%)are obtained in the alloy containing the bimodal grain distribution.The discontinuous dynamic recrystallization(DDRX)mechanism is the prominent grain refinement mechanism in the alloy subjected to 2 passes of HSRR.

Effect of welding speed on microstructure and mechanical properties of Al−Mg−Mn−Zr−Ti alloy sheet during friction stir welding

Effects of welding speed on the microstructure evolution in the stir zone(SZ)and mechanical properties of the friction stir welding(FSW)joints were studied by OM,XRD,SEM,TEM,EBSD and tensile testing.Compared with the base metal(BM),an obviously fine dynamic recrystallization(DRX)microstructure occurs in the SZ and the DRX grain size decreases from 5.6 to 4.4μm with the increasing of welding speed.Fine DRX microstructure is mainly achieved by continuous dynamic recrystallization(CDRX)mechanism,strain induced boundary migration(SIBM)mechanism and particle stimulated nucleation(PSN)mechanism.Meanwhile,the geometric coalescence and the Burke−Turnbull mechanism are the main DRX grain growth mechanisms.Among all the welding speeds,the joint welded at rotation speed of 1500 r/min and welding speed of 75 mm/min has the greatest tensile properties,i.e.ultimate tensile strength(UTS)of(509±2)MPa,yield strength(YS)of(282±4)MPa,elongation(El)of(23±1)%,and the joint efficiency of 73%.

Dynamic recrystallization and mechanical properties of high-strain-rate hot rolled Mg-5Zn alloys with addition of Ca and Sr

Effects of the sole and the combined addition of Ca and Sr on microstructure and mechanical properties of as-cast and as-rolled Mg-5 Zn alloys were carefully investigated by OM,SEM,hot-compression testing and tensile testing.Ca is more effective than Sr in the microstructural refinement of as-cast alloys.High-strain-rate rolling(HSRR)produces more deformed twins and thus provides more nucleation sites for dynamic recrystallization(DRX).The addition of Ca and Sr can promote dynamic precipitation during HSRR,the precipitation process would consume the storage energy and thus increases the critical strain value of DRX,resulting in the retarded DRX effect by the addition of Ca and/or Sr.The as-rolled Mg-5 Zn-0.4 Ca-0.2 Sr alloy exhibits a good combination of strength and ductility,with the ultimate tensile strength of 317 MPa,the yield strength of 235 MPa and the elongation to rupture of 24%.

Solid solution strengthening and damping capacity of Mg-Ga binary alloys

The mechanical behaviors and damping capacities of the binary Mg−Ga alloys with the Ga content ranging from 1 to 5 wt.%were investigated by means of optical microscope(OM),scanning electron microscope(SEM),X-ray diffraction(XRD),hardness test,tensile test and dynamic mechanical analyzer(DMA).The hardness(HV_(0.5))increases with the increase of Ga content,which can be described as HV_(0.5)=41.61+10.35c,and the solid solution strengthening effect∆σ_(s)of the alloy has a linear relationship with c^(n),where c is the molar fraction of solute atoms and n=1/2 or 2/3.Ga exhibits a stronger solid solution strengthening effect than Al,Zn or Sn due to the large atomic radius difference and the modulus mismatch between Ga and Mg atoms.The addition of Ga makes the Mg−Ga alloys have better damping capacity,and this phenomenon can be explained by the Granato−Lücke dislocation model.The lattice distortion and the modulus mismatch generated because of the addition of Ga increase the resistance to motion of the dislocation in the process of swinging or moving,and thus the better damping capacity is acquired.

Microstructure characteristics and liquation behavior of fiber laser welded joints of Mg-5Zn-1Mn-0.6Sn alloy sheets

Fine-grained Mg?5Zn?1Mn?0.6Sn alloy sheets of2mm in thickness were welded by fiber laser welding.The appearanceand microstructures of the welding joints and liquation behaviors in the partially melted zone(PMZ)were investigated.The resultsshow that,with the lower welding power and higher welding speed,the width and depth of the joints decrease.Moreover,some poresare detected at a very high welding speed.There are two kinds of liquation phenomena in the PMZ.One is the liquation networkalong grain boundaries associated with the liquation of substrate and segregation-induced liquation,the other is the molten poolinvolved with the liquation of the residual second phases at the boundaries.However,the liquation of substrate and thesegregation-induced liquation are the main liquation mechanism in the PMZ.

Microstructure and mechanical properties of friction-stir-welded high-Mg-alloyed Al-Mg alloy plates at different rotating rates

Hot-rolled high-Mg-alloyed Al-Mg alloy(Al-9.2 Mg-0.8 Mn-0.2 Zr-0.15 Ti,labeled as 5 A12)plates were successfully friction stir welded at rotating rates ranging from 750 to 1500 r·min^(-1) at a constant welding speed of50 mm·min^(-1).The joints were characterized by optical microscopy(OM),electron backscatter diffraction(EBSD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),electron-dispersive spectroscopy(EDS),and tensile testing.All the joints are volume defectfree and exhibit fine,equiaxed dynamic recrystallization(DRX)grains with high-angle grain boundaries(HAGBs)fractions of 88.6%-93.3%in the nugget zones(NZs).The DRX grain size and the second-phase particle size in the NZs have a parabolic relation with the rotating rate.Furthermore,among the joints tested,the joint prepared at1000 r·min^(-1),which has the highest ultimate tensile strength((478±3)MPa)and the largest elongation to rupture(22.5%±1.4%)—approximately 87.5%and145.2%those of the base metal,respectively,exhibits the smallest grain size of 2.93μm,as well as the smallest particle size in the NZs.These excellent mechanical properties can be ascribed to the combined effects of the fine DRX grains with high fraction of HAGBs and the fine second-phase particles with a uniform distribution.