Investigation On Extraction Technology For Alloy Phases In AZ And ZK Magnesium Alloys

One of the difficulties in the identification of magnesium alloy phases is the lacking of qualitative and accurately quantitative analysis means approporiate to the second phases in magnesium alloys, which leads to the shortage of knowledge including the evolution for some phases in magnesium alloys. The research objective of the dissertation is to employ the electrolytic extraction technology to the research of magnesium alloys, and to establish the test methods for the precise identification and accurately quantitative analysis for the phases in magnesium alloys. The research results will helpfully offer an effective analysis means to the evolution of alloy phases in magnesium alloys, which may promote the study of the alloying of magnesium alloy and so the development and application of magnesium.In this dissertation, the extraction technology for Al-Mn phases andβphase in AZ magnesium alloys has been developed successfully, so for the MgZn₂ phase in ZK magnesium alloys. The extraction technology Mg-Zn-Y magnesium alloys has also been put forward.Potentiostat is one of the principal instruments for the precise process control of anode solution during electrolytic extraction. A prototype instrument based on chip microcomputer control technology was developed in this work, and both the digitized design scheme and the digital compensation concept are put forward. Besides in detail several test methods were introduced, which includes the potentiostatic extracting of magnesium alloy phases, fabricating of anode and cathode samples, collecting of remnant compound powders extracted from magnesium sample and its analysis methuals including X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX).In this dissertation, the extraction technology for Al-Mn phases andβphase in AZ magnesium alloys has been developed successfully, so for the MgZn₂ phase in ZK magnesium alloys. The extraction technology Mg-Zn-Y magnesium alloys has also been put forward.The results show that using the acetic acid water of 1:10 ratio facilitates the extracting of Al-Mn phases from AZ magnesium alloys, which is used to extract the Al-Mn phases from the as-cast, as-rolled and as-extruded AZ31 and AZ61 magnesium alloys. XRD analysis shows that manganese exists in both the way of Al8Mn5 phase and dissociated manganese particles in the AZ magnesium alloy, and rolling or extrusion processing does not change the type of the Al₈Mn₅. SEM observation shows that Al8Mn5 phases are formed mainly in dendrite and leaf shape with size of 15-100μm in the as-cast AZ magnesium alloys, and are broken into fine spherical fragments with size of about 4-5μm after rolling or extrusion. The dissociated manganese particles, which are co-existed with cubic-shaped Al-Mn phases or flower-shaped Al-Mn phases, are thought to be the nucleus of cubic-shaped Al-Mn phases.The study of the extractingβ-phase from the AZ magnesium alloys shows that utilizing the ammonium benzoate - acetic acid - abietite acid - ethanol electrolyte can single out theβ-phase, but produce the deposition, such as magnesium acetate hydrate and zinc acetate hydrate, which is difficult to be dispart from theβ-phase particles. The study also indicates that adding complexation and chelating agent of magnesium such as citric acid, DDTC and F- to the electrolyte can not inhibit the deposition. Adding the ethylene glycol can inhibit the deposition, but addititional unidentified substance appears on the surface of anode. Furthermore, it shows that controlling the electrolyzation quantity of electricity for the electrolyte with the addition of the dioxane can prevent the depositing of magnesium acetate hydrate and zinc acetate hydrate from the electrolyte.The study of the extracting of alloy phases from the Mg-Zn-Zr magnesium alloys shows that utilizing the o-aminobenzoic acid - acetic acid - ethanol liquor and ammonium benzoate - acetic acid - ethylene diamine - ethanol electrolyte can extract MgZn₂ phase from the as-cast ZK60 magnesium alloy, and utilizing the o-aminobenzoic acid - acetic acid - ethanol liquor can extract Mg₃Y₂Zn₃ phase from the as-cast Mg-6.0Zn-0.6Zr-1.0Y magnesium alloy. But due to the negative variance effect of magnesium alloy, Zn ion in the solution is reduced to Zn atom on the surface of the test samples, which can be identified among the separated residues. Adding ethylene diamine, the complexation of Zn, to these electrolyze can definitively prevent the formation of Zn when low electrolyzation quantity of electricity is employed, but can not prevented completely employing over electrolyzation quantity of electricity. The results also indicate that Zn atom can not be prevented completely when electrolyzed above Zn decomposing potential.The study of the electrolyzation extracting for the Mg-Zn-Y magnesium alloy shows that utilizing picric acid - cetic acid - ethanol electrolyte can extract the phases of Mg₃Y₂Zn₃, Mg₁₀Y₂Zn, Mg₃YZn₆ and the quasi-crystal Mg-Zn-Y from the as-cast Mg-6.0Zn-0.6Zr-1.0Y magnesium alloy. The same results can be found when utilizing DDTC - 2,2'-bipyridine - salicylic acid - dioxane - methanol electrolyte, but the deposition which is difficult to be separated produces. Utilizing the picric acid - cetic acid - ethanol electrolyte, the alloy phases have been extracted from the as-cast Mg-6.0Zn-1.2Y, the as-aged Mg-6.0Zn-1.2Y, the as-cast Mg-6.0Zn-1.0Y-0.6Zr and the as-aged Mg-6.0Zn-1.0Y-0.6Zr, respectively. The XRD results show that the structure of the Mg₃Y₂Zn₃ phase contained in the as-cast Mg-6.0Zn-1.2Y and Mg-6.0Zn-1.0Y-0.6Zr alloy does not changed after solution and aged treatment, and the Mg₁₀Y₂Zn phase, Mg₃YZn₆ phase and the quasi-crystal Mg-Zn-Y phase disappares. In the Zr-contained magnesium alloys, Zr exists in the form of ZrO2 compound in the extracted residues.