Ji Qiang Li

Microstructure and Mechanical Properties of Lost Foam Casting AZ91D Alloy Produced with Mechanical Vibration

Mechanical vibration was introduced into the solidification in order to overcome the defects of coarse microstructure and low mechanical properties of the AZ91D magnesium alloy via lost foam casting（LFC）. The microstructure with fine uniform dendrite grains were achieved with mechanical vibration, which was mainly attributed to the cavitation and the melts flow induced by the mechanical vibration. The mechanical vibration has strong influence on the mechanical properties of AZ91D alloy. With application of mechanical vibration, the ultimate tensile strength and elongation of the AZ91D alloy increase 23% and 26%, resepectively.

Influence of Process Papameters by Vibrational Cooling-Shearing Slope on Microstructures of Semi-Solid ZAlSi9Mg Alloy

An experimental vibrational cooling-shearing slope was developed to prepare the ZAlSi9Mg semi-solid alloy. The results show that the molten alloy is nucleated heterogeneously under shearing of the gravitation and vibration on the inclined cooling plate surface. Primary α-Al phase converts gradually from the cellular dendrite into tiny spherical or granular crystal. Under 600°C of pouring temperature, 600mm of casting length and 50Hz of vibration frequency, the semisolid alloy melt with good microstructure can obtained. In the alloy melt the average grain size of the original α-Al phase is 50μm, and its shape factor is 0.71. Mechanical vibration can refine obviously the microstructure of ZAlSi9Mg alloy. Along with increasing of vibration frequency, the original α-Al phases are refined obviously, their roundness is improved.

Study on Microstructure of Semi-Solid Magnesium Alloy Manufactured by Gas Bubbles Stirring

The semi-solid slurry of AZ31 magnesium alloy was manufactured by gas bubbles stirring. The effects of stirring temperature and stirring time on the microstructure of semi-solid slurry were researched. The results indicate that it is feasible to manufacture the slurry with particle-like primary phases. When the stirring temperature is higher, the morphology of the primary a-Mg presents rosette-like morphology and the size of grain is coarse, and the morphology mainly was α- Mg dendrite at lower stirring temperature. Long stirring time could reduce dendrites and liquid phase, and made the non-dendritic grains well spheroidized. But the effects of longer stirring on shape and size of primary particles are not significant. The optimal process parameters for ideal semi-solid slurry manufactured were stired 3min at 645°C.

Study on Formability of Tailor Welded Blanks Based on Numerical Simulation

The strength ratio, thickness ration of blanks and the microstructure of weld seam play important role in the formability of tailor welded blanks (TWB). With numeric simulation technology in different conditions such as different thickness and different strength combination of TWB’s materials, the forming limit depth (FLD) of tailor welded blanks is analyzed. The affect of the thickness ratio and strength ratio on forming limit depth is investigated, the laws influencing the formability of TWB square box are summarized, and approaches are presented to increase the FLD. The results of simulation and practice indicate that reducing the difference of the thickness ratio, choosing lower strength material for thicker blank, and adopting right heat treatment can improve the forming limit depth. Keywords: Tailor Welded Blanks; Forming Limit Depth; Thickness Ratio; Strength Ratio

Die-Casting Die Design Based on the Application of CAE Simulation

High pressure die casting is a high volume component manufacturing process which is used extensively in many aspects. There are many factors affecting the quality of die-casting die. In this paper, the CAE simulations of filling and solidification processes for die-casting are studied. Numerical analyses are presented for two practical die-casting parts using HZ CAE software. The temperature distributions and filling states in solidification and filling process are presented. Then the deficiencies of the part are predicted. Based on the analyzing results, the structures of the two dies are optimized and longer die service life and high-quality castings are obtained. It is proved that CAE simulation results can offer a helpful reference for die-casting die design.

Local Laser Bionic Blocking Experimental Study of Hot Work Mould Surface Cracks

For the short life of hot work die in enterprise directly caused problems the waste of resources and the rising cost of production. Based on studying the biological prototype of crack-resistance of plant lamina and found that surface thermal fatigue crack is one of the main factors affecting the service life of hot work mould, it is put forward thoughts about the local bionic laser melting on mould surface to block cracks. Different from the traditional mould surface integral laser transformation hardening (LTH) technology, using laser melting simulating plant lamina to block cracks on the partial surface of mold, life of bionic strengthened die is improved within 1~1.5 times. Experiment results show that a new method is provided to improve the service life of casting mould and promoting this technology will bring significant economic benefits for the mould industry.

Study on the Cavity Defects of Low-Pressure Lost Foam Casting for Magnesium Alloy

Cavity defects of low-pressure lost foam casting (LP-LFC) for magnesium alloy were investigated by using ladder samples and claviform samples.The physical feature of typical cavity defects of LP-LFC for magnesium castings had been tested by optical microscopy and scanning electron microscopy. And the chemical constitution of cavity surface was also tseted by energy spectrometer. The result indicated that the cluster cavity defects were formed with the application of higher vacuum at the metal-mold interface, which caused the liquid-EPS residue in the castings. Some irregular shape cavity defects were caused by slag entrapment or coating slough. These cavity defects could be avoided through reducing pouring temperature, filling velocity and vacuum level, improving the permeability of coating.

Determination of Optimal Temperature for Defect-Free Casting of Aluminium in the LP-LFC Process

Fluidity of ZL101 aluminium alloys in the low-pressure lost foam casting (LP-LFC) process has been investigated by altering various temperature variables. The experimental results indicate that the LP-LFC process had fine fluidity, and the pouring temperature was lower than conventional lost foam casting. The effect of the metal temperature on the fluidity is marginal in the LP-LFC process. Excessive pouring temperature not only aggrandizes energy consumption but also deteriorates porosity defect. The success of casting cooling fin demonstrates the advantages of LP-EPC process in producing high-complicated castings.

Development of Microstructure of Semi-Solid A356 Alloy by Alternating Electromagnetic Stirring

The influence of processing parameters on the semi-solid microstructure has been investigated in the course of semi-solid slurry preparation of A356 aluminum alloy by alternating electromagnetic stirring. The results show that compared with horizontal, vertical and spiral magnetic stirring method, alternating magnetic stirring could make eligible slurry with finer, more equiaxed and more homogeneous primary α particles in much shorter time. The microstructure evolution during isothermal treatment is studied and it is shown that the average particle diameter increases with the holding time and the shape coefficient decreases somewhat at first, and then decreases sharply in the end. It is discovered that alternating electromagnetic stirring is a good method to prepare semi-solid slurry with fine and relatively round primary particles.

Formation of Non-Dendritic Microstructure of Semi-Solid Magnesium Alloy by Introducing Gas Bubbles

A new technique of introducing gas bubbles during isothermal period of AZ31 magnesium to prepare semi-solid slurry has been reported. The effect of resting time after stirring on the microstructure of the slurry is discussed. Results show that the dendrites and liquid phase reduced, the non-dendritic grains grew up and became spheroidized. A fully grain-refined structure can be obtained with 60s resting time.