Effect of Zn, Cu and Ni addition on microstructure and mechanical properties of ascast Mg-Dy alloys

This paper presents some research information on the effects of Zn, Cu and Ni on the microstructure and mechanical properties of as-cast Mg-2Dy(at.%) alloys. The Mg-2Dy alloy is composed of α-Mg and Mg24Dy5 phases. With the addition of 0.5at.%Zn, 0.5at.%Cu and 0.5at.%Ni, respectively, besides α-Mg, the long period stacking order(LPSO) phases containing Zn, Cu, and Ni precipitated in the α-Mg interdentritic boundary. The addition of Ni effectively refined the dendrite arm spacing. The as-cast Mg-2Dy-0.5Ni alloy exhibited the best tensile strengths and elongation. The better mechanical properties were mainly attributed to small secondry dendrite arm spacing(SDAS) and high volume fraction of LPSO phases.

Microstructure characteristics and solidification behavior of wrought aluminum alloy 2024 rheo-diecast with self-inoculation method

One important problem in casting wrought aluminum alloys is the high tendency to the formation of hot tears in the solidification process.By using semi-solid metal(SSM) processing,the hot tearing tendency of alloys can be minimized during casting.In the present research,the semi-solid slurry of wrought aluminum alloy 2024 was firstly prepared with a novel self-inoculation method(SIM),and then the microstructure characteristics of the semi-solid slurry and the rheo-diecastings cast with the semi-solid slurry were investigated.The results indicate that finer and more uniform globular primary α-Al particles can be obtained when the semi-solid slurry are isothermally held for a short period within the semi-solid temperature range,and the primary α-Al particles without entrapped liquid are uniformly fine,globular grains in the rheo-diecastings.The holding temperature and time affect the solid fraction,particle size,and shape factor.After the semi-solid slurry is held at 625 ℃ for 3 min and 5 min,the optimal values for the average equivalent diameter are 70.80 μm and 74.15 μm,and for the shape factor are 1.32 and 1.42,respectively.The solidification process of the rheo-diecastings is composed of the following two distinct stages:primary solidification process and secondary solidification process.The secondary solidification process consists further of the following three stages:(1) direct growth of secondary primary(α 2) phase from the surface of the primary α-Al phase particles without re-nucleation,(2) independent nucleation and growth of α 3 phase from the residual liquid,and(3) eutectic reaction at the end.

Effects of melt treatment temperature and isothermal holding parameter on water-quenched microstructures of A356 aluminum alloy semisolid slurry

The semisolid slurry of the A356 aluminum alloy was prepared by self-inoculation method(SIM),the effects of melt treatment temperatures and isothermal holding parameters on water-quenched microstructures of A356 aluminum alloy semisolid slurry were investigated,and the solidification behavior of the remaining liquid phase(secondary solidification)was analyzed.The results indicate that the melt treatment temperature has significant effects on the final semisolid microstructures.The semisolid slurry which is suitable for the rheological forming can be produced when the melt treatment temperature is between 680 and 690°C.During the isothermal holding process,the growth rate of the primary particles conforms to the dynamic equation of Dt 3-Do3=Kt,and the coarsening rate of the primary particles is the fastest when the isothermal holding temperature is 600°C.Additionally,the isothermal holding time also has obvious effect on the secondary solidification microstructures.The secondary particles are the smallest and roundest when the isothermal holding time is 3 min.The amount of the secondary particles gradually increases with the increase of isothermal holding temperature,and the eutectic reaction therefore is confined into small intergranular areas,contributing to the compactness of the final solidified eutectic structures.

Commercial AM60 alloy for semisolid processing:Effects of continuous rheoconversion process on microstructure

In order to verify the effect of CRP(continuous rheoconversion process) in the preparation of magnesium alloy semisolid billets,AM60 alloy billets were fabricated with CRP,and effects of pouring temperature,slope angle,and length of the reactor on the microstructure of AM60 alloy were investigated.The results show that the grain size is reduced with the decrease of pouring temperature.A small block/rosette grain is obtained when the pouring temperature is less than 680 °C.Therefore,the available temperature process interval/window has to be required.To change slope angle of reactor(from 30° to 45°) is helpful for formation of the small and block/rosette grains.Meanwhile,the reactor with a length of 500 mm is enough for copious nucleation of primary phase.CRP changes the solidification microstructure of billets by controlling the nucleation and growth of the primary phase in melt.

Commercial AM60 alloy for semisolid processing:Alloy optimization and thermodynamic analysis

Semisolid processing is now a commercially successful manufacturing route to produce net-shape parts in automotive industry. The conspicuous results of alloy optimization with thermodynamic simulations for semisolid processing of commercial AM60 alloy were present. The results indicate that the available processing temperature range of AM60 alloy is 170 ℃. The temperature sensitivity of solid fraction decreases with increasing solid fraction or with decreasing temperature above eutectic reaction temperature of AM60 alloy. When the solid fraction φs is 0.4, corresponding processing temperature is 603.8 ℃ and the sensitivity -dφs/dT is 0.0184. The effects of various alloying elements on the solidification behavior and SSM processability of AM60 alloy were calculated with Pandat software.

Effect of heat treatment on microstructure and properties of single crystal copper cold-welded joints

With the means of electron backscattered diffraction(EBSD),mechanical properties test and digital eddy current metal conductivity,the single crystal copper cold-welded joint was tested and analyzed,the structure change of cold-welded joint and the effect of heat treating on the structure and property of cold-welded joint were discussed.The results show that:The deformation area of the single crystal copper cold welded joint is broken,the crystalline grain at the interface of the joint is refined,and the single crystal structure is still maintained in the base metal area.The hardness of the deformation area increases greatly,the conductivity of the joint does not change much,and the tensile strength of the joint reaches about 70%of that of the base metal.At the interface of the heat treating joint,the single crystal structure of the deformation area and the base metal area are destroyed,and the grains grow up at the interface and the orientation is different.The hardness of the joint interface is much lower than that of the non-heat treating joint,the electrical conductivity of the joint is good,and the tensile strength of the joint is higher than that of the base metal.

Microstructure of partially remelted billet of AM60 alloy prepared with self-inoculation method

The billets of AM60 alloy, prepared with self-inoculation method, were partially remelted into semisolid state. Effects of process parameters on remelting microstructure of semisolid billet were investigated. Experimental results show that the solid particles obtained with self-inoculation method are in smaller grain size and globular shape after partial remelting, compared with those prepared with other casting methods. In the optimized process conditions, the average size of solid particles of partially remelted billet is 65 μm, and the shape factor is 1.12. The process parameters, i.e. pouting temperature, addition amount of self-inoculants, and the slope angle of multi-stream mixing cooling chalmel have influence on the microstructure of partially remelted billet. The optimized temperature is from 680 ℃ to 700 ℃, addition amount of self-inoculants is between 5% and 7% （mass fraction）, slope angle of multi-stream mixing cooling channel is between 30° and 45°, with which the dendritic microstructure of as-cast billet can be avoided, and the size of solid particles ofremelted billet is reduced.

Microstructure evolution and corrosion properties of Mg-Dy-Zn alloy during cooling after solution treatment

Microstructure evolution and corrosion properties of Mg-2Dy-0.5Zn （at.%） alloy during cooling after solution treatment were investigated. The microstructure of alloy in the solid solution state （530 oC, 12 h） was composed ofα-Mg and small amounts of （Mg, Zn）xDy phases. During cooling at a cooling rate of 2 oC/min, the 14H-type LPSO phase gradually precipitated in the grain inte-rior and its volume fraction increased with increasing cooling time. The alloy cooled for 20 min exhibited the highest hardness value. In addition, electrochemical and immersion test results indicated that the alloy cooled for 5 min exhibited small corrosion current and low corrosion rate. The good corrosion resistance of alloy was mainly attributed to the continuous distribution of LPSO phase along the grain boundary.

Microstructural evolution and age-hardening behavior of quasicrystal-reinforced Mg-Dy-Zn alloy

Microstructural evolution and age-hardening behavior of Mg-2 Dy-6 Zn(at%)alloy during solid-solution and aging treatment were investigated.The microstructure of as-cast alloy is composed of a-Mg,Mg3 DyZn6(Ⅰ)phase,Mg3 Dy2 Zn3(W)phase,Mg(Zn,Dy)phase and a small amount of Mg0.97Zn0.03 phases.After solid-solution treatment(480℃,12 h),all the I phases and most W phases dissolve into a-Mg matrix and the remainder W phases transform into Mg(Dy,Zn)phase and MgDy3 phase.During aging treatment,I phase and small amounts of W phases co-precipitate from α-Mg matrix,respectively.The alloy exhibits a peak hardness of HV 77.5 at 200 ℃ for 8 h.The excellent age-hardening behavior of alloy is mainly attributed to the co-precipitation strengthening of I and W phases.

Microstructure evolution and mechanical properties of 316L austenitic stainless steel with aluminum addition by warm rolling

Microstructure evolution and mechanical properties of 316L austenitic stainless steel with aluminum addition by warm rolling at 550 ℃ were investigated. It is found that sample is composed of an ashen austenite matrix, a gray black ferrite phase and a small number of NiCx. The average grain sizes are 21.62, 19.66 and 19.49 μm for samples with the rolling deformation of 30%, 50% and 70%, respectively. The yield strength and tensile strength of samples with solid solution time of 30 min and deformation of 70% are higher. The fracture modes are similar and belong to toughness fracture. The fracture surfaces of the samples are composed of relatively large equal-axis ductile dimples （5-15 μm） and fine scattered ones around the dimples （〈 5 μm）. As the rolling deformation increases, the quantity of subgrain boundary increases and the 〈 101 〉 orientation is more prominent. {001 } 〈 110 〉 rotation-cube textures are present in ferrite phase of samples and weak Goss texture is formed in austenite pole images.