Microstructures and Key Properties of Mechanically Deposited Zn-Al Coatings

Zn-Al coatings can provide protection to exposed steel parts in most environments. For this reason, the investigation of Zn-Al coatings become very popular in recent years. In order to study the microstructures and properties of mechanically deposited Zn-Al coating, zinc powders and aluminum powders were used to deposit Zn-AI coating by mechanical plating. The microstruetures, phase constitutes and compositions of the coating were observed and analyzed with optical microscopy （OM）, scanning electron microscopy（SEM）, X-ray diffraction（XRD） and X-ray energy-dispersive spectroscopy（EDS）. The results of observation show that the coating consists of almost spherically shaped zinc particles point contacting with each other; the coatings are composed of zinc particles, aluminum particles, interstice, and tin; extra fine zinc powders and some smaller interspersed inclusions are positioned in the interstices. Porosity and thickness of the coating were tested by ferroxyl test and magnetic method. The corrosion resistance of coatings was studied by neutral salt spraying test（NSS）, immersion test and electrochemical polarization. It is found that the thickness of the coating dose lacks uniformity, with an uneven thickness distribution and an average variation of approximately 2-5gm; the coating can afford cathodic protection to the steel substrate; the corrosion resistance of Zn-Al coatings is better than that of the mechanically plated zinc coatings with same thickness. These conclusions can be applied to improve anti-corrosion performance by mechanically deposit Zn-Al coatings.

Experimental Study on the Flow Characteristics of a Plate with a Mechanically Choked Orifice

The mechanically choked orifice plate (MCOP) is a new type of device for flow control by which choking conditionsfor incompressible fluids can be obtained with relatively small pressure losses. Given the lack of relevant results anddata in the literature, in the present study, we concentrate on the experimental determination of the flow coefficientfor the annular orifice, the pressure distribution in the MCOP, and the characteristics of the choked flow itself. Asconfirmed by the experimental results, the Reynolds number, the orifice plate thickness, the plug taper, and theeccentricity have an obvious influence on the aforementioned flow coefficient. The pressure drop in the MCOPis mainly generated near the orifice plate, and the pressure upstream of the orifice plate is slightly reduced in theflow direction, while the pressure downstream of the orifice plate displays a recovery trend. The choked flow rateof the MCOP can be adjusted by replacing the spring with a maximum flow control deviation of 4.91%.

MECHANICAL VIBRATIONAL POWER FLOW IN BEAM-PLATE ASSEMBLIES

The vibrational power flow in the beam-plate assemblies and then with the isolators is investigated using analytical ' power flow' approach based on the some concepts of mechanical mo- bility and structural dynamics. Theoretical expressions of the power flow in the structures are given and examined. The numerical results of the expressions are good agreements with the measuring re- sults obtained by the technique of vibration intensity. On the basis of these results, possible ways of reducing the vibrational power flow in the structures are suggested .

METAL SURFACE MODIFICATION──RESEARCH OF BRUSH PLATING TECHNOLOGY OF CrLAYER

Trivalen t Cr layers are studied by direct current brush- plating and pulse current brush-plating. Under the SEM,the appearence,the morphology of cross sections and normal sec- tions of the layers are observed and analysed,the hardness, bond intensities and corrosion- resis- tance are measured. Then, the election- probe and X ray diffraction instruments are used to study the bond and harden mechanism of lavers,The result of research shows that: the harden ef- fect of the layers is caused by the extra- fine grains and internal stress in the layers. And the lay- ers and basis are joined by mechanical bond,metal bond and diffuse bond. All these kinds of bonds lie on different places of interface, they make the layers and base metal unit well.

Inhomogeneity of microstructure and mechanical properties in the nugget of friction stir welded thick 7075 aluminum alloy joints

In this study, 20 mm thick AA7075-T6 alloy plates were joined by friction stir welding. The microstructure and mechanical properties of the nugget zone along the thickness direction from the top to the bottom was investigated. The results showed that the microstructure including the grain size, the degree of dynamic recrystallization, the misorientation angle distribution and the precipitation phase containing its size, type and content exhibited a gradient distribution along the thickness direction. The testing results of mechanical properties of the slices showed that the nugget was gradually weakened along the depth from the top to the bottom. The maximum ultimate tensile strength, yield strength and elongation of the slice in the nugget top-middle are obtained, which are 415 MPa, 255 MPa and 8.1%, respectively.