Precipitation modification in cast Mg-1Nd-1Ce-Zr alloy by Zn addition

The effects of different Zn addition(0,0.2,0.5,1.0 wt%)on the microstructure and mechanical properties of cast Mg-1Nd-1Ce-Zr alloy in as-cast,solution-treated and 200℃peak-aged conditions were studied.Precipitates in cast Mg-1Nd-1Ce-Zr alloy are significantly modified by the Zn addition.In the Zn-free alloy,the disk-shaped prismatic precipitates and the point-like precipitates are the main strengthening phases.When 0.2 Zn is added,the disk-shaped precipitates are refined and very fine basal precipitates form additionally.When 0.5 Zn is added,the basal precipitates become the main strengthening phase.Further increasing the Zn addition to 1.0%,only spare basal precipitates and point-like precipitates exist.The 0.5 Zn addition alloy has the highest strength at room temperature,whose yield strength,ultimate tensile strength and elongation in T6 condition are 136 MPa,237 MPa and 9%,respectively.

Effects of minor Zn content on microstructure and corrosion properties of Al-Mg alloy

The effects of different Zn contents in Al-Mg alloy on the microstructure characterizations were observed by advanced electron microscopy and the corrosion properties were investigated by the inter-granular corrosion tests,the exfoliation corrosion tests,and the Potentiodynamic polarizaion tests.The τ phase(Mg_(32)(Al,Zn)_(49)) forms on the pre-existing Mn-rich particles and at the grain boundaries.According to the theory of binding energy,the formation of τ phase is much easier than that of β phase(Al_3Mg_2),somehow replacing β phase and reducing the possibility of β phase precipitation.This change dramatically decreases the susceptibility of corrosion.The Zn addition increases the corrosion resistance of Al-Mg alloy with an optimal value of 0.31%.When the Zn addition is increased to 0.78%,however,the corrosion resistance of alloy decreases once again but it is still better than that of the alloy without Zn addition.

BrCo (dmgh)_2Py/Zn Promoted Addition of BrCF_2CF_2CH=CHCH_2X to Alkynes: Direct Synthesis of 4,4,5,5-Tetrafluorocyclopentene Derivatives

BrCF2CF2CH=CHCH2X(x=Cl, OAc, OH) reacted smoothly with alkynes in the presence of BrCo(dmgh)2Py/Zn, giving 4,4,5,5-tetrafluorocyclopentene derivatives in moderate yields.

Atomic-scale roles of Zn element in age-hardened AlMgSiZn alloys

Adding alloying elements to improve the performances or the manufacturing processes of Al-Mg-Si alloys has long been a serious issue in developing advanced automotive aluminum materials.The Zn element,among those promising ones,has demonstrated positive alloying effects on Al-Mg-Si alloys.However,the atomic-scale roles of Zn in an age-hardened Al-Mg-Si-Zn alloy have not been adequately understood.Using atomic-resolution electron microscopy,here we report the precise locations of Zn elements in all hardening precipitates involved and their alloying mechanism at the atomic scale when alloying the alloy.Our results show that Zn atoms enter all the major hardening phases to occupy specific featured atomic sites of the original elements,e.g.the Si1 and Mg2 sites in theβ’-2 phase,and modify their crystal structures,interfacial structures and morphologies in characteristic manners.It is revealed that for theβ’-phase,Zn atoms occupy unique atomic sites,whereas for other phases,they demonstrate similar behaviors as other additive alloying elements such as Ag and Cu do.

Transformation behavior of precipitates during artificial aging at 170℃in Al-Mg-Si-Cu alloys with and without Zn addition

The transformation behavior of precipitates in Al-Mg-Si-Cu alloys with and without Zn addition during artificial aging at 170℃was investigated in this study.For Al-Mg-Si-Cu alloys with and without Zn addition,two types of precipitates,needle-likeβ″and lath-like L,are formed with the aging time increasing from 8 to 34 h.The needle-likeβ″precipitate exhibits a Mg-to-Si atomic ratio of 1.31 which is in agreement with the theoretical ratio of1.25 forβ″(Mg5 Al2 Si4).In addition,theβ″precipitate is supposed to contain Al and Cu.With further partitioning of Mg,Si and Cu and release of Al,the needle-likeβ″precipitate can transform to lath-like L phase.The L phase has significantly higher concentrations of Mg,Si and Cu and lower concentration of Al,with a higher Mg-to-Si atomic ratio(1.41)deviated from theoretical ratio ofβ″.However,the major of Zn has a random distribution in Al matrix and exhibits no significant partitioning into precipitates.Zn remained in matrix can enhance the transformation ofβ″precipitates to L precipitates.

Microstructural Characteristics and Mechanical Properties of Cast Mg–3Nd–3Gd–xZn–0.5Zr Alloys

The microstructure,aging behavior and mechanical properties of cast Mg–3Nd–3Gd–x Zn–0.5Zr(x=0,0.5,0.8,1 wt%)alloys are investigated in this work.Zn–Zr particles with different morphologies form during solution treatment due to the additions of Zn.As the Zn content increases,the number density of Zn–Zr particles also increases.Microstructural comparisons of peak-aged studied alloys indicate that varying Zn additions could profoundly influence the competitive precipitation behavior.In the peak-aged Zn-free alloy,β′′phases are the key strengthening precipitates.When 0.5 wt%Zn is added,besidesβ′′precipitates,additional fineβ_(1)precipitates form.With the addition of 0.8 wt%Zn,the peak-aged 0.8Zn alloy is characterized by predominantly prismaticβ_(1)and scanty basal precipitate distributions.The enhanced precipitation ofβ_(1)should be primarily attributable to the presence of increased Zn–Zr dispersoids.When Zn content further increases to 1 wt%,the precipitation of basal precipitates is markedly enhanced.Basal precipitates andβ_(1)phases are the key strengthening precipitates in the peak-aged 1Zn alloy.Tensile tests reveal that the relatively best tensile properties are achieved in the peak-aged alloy with 0.5 wt%Zn addition,whose yield strength,ultimate tensile strength and elongation are 179 MPa,301 MPa and 5.3%,respectively.

Diverse synthesis of the C ring fragment of bryostatins via Zn/Cu-promoted conjugate addition of α-hydroxy iodide with enone

A convergent approach to 1,5-hydroxy ketones,the general precursors for constructing the C ring of bryostatins,has been developed via a Zn/Cu-promoted conjugate addition of a-hydroxy iodides with enones.The reaction leads to direct formation of the C21-C22 bond and tolerates diverse functionalities at the C17-,C18-and C24-positions.The approach also enables a more concise synthesis of the known C ring intermediate(10 longest linear steps and 14 total steps),in contrast to its previous synthesis(17 longest linear steps and 22 total steps) in our total synthesis of bryostatin 8.