Experiment And Mechanism Research On Al-Water Reaction Of Dissolvable Al Alloy

The fracturing tools made of dissolvable aluminium alloys have very important applications in hydraulic fracturing which is widely used for well stimulation.The dissolvable aluminium alloys as a structural material should possess excellent mechanical properties?tensile strength,plasticity?besides its dissolving properties.Although adding strengthening elernents?Mg,Cu?in alloy,heat treatment and grain refinement will improve the mechanical properties of alloys,but it is no doubt that these methods will markedly affect the dissolving properties of alloys as they improve the mechanical properties of alloys.The prominent problem is the formation of many kinds of interfacial phases containing Mg and low melting point metals,so that the mechanism of Al-water reaction?liquid interfacial phase theory?suited for Al-Ga-In-Sn alloys is invalid for Mg containing Al alloys.Therefore,this is an issue deserved to investigate.Additionally,the addition of grain refiner Al-5Ti-1B and hardening elements Cu in alloys will influence the microstructures of alloys.These issues are also deserved to investigate.In the present dissertation,series of dissolvable aluminium alloys were prepared by using casting metallurgy method.Their microstructures were characterized by XRD and SEM/EDX.The Volta potential difference?AVPD?between the interfacial phases and Al matrix was measured using scanning kelvin probe force microscopy?SKPFM?.The electronic density of states and chemical bond of interfacial phase crystal of Al-Mg-Ga-In-Sn alloys are calculated using the First Principle Theory.The Al-water reactions of alloys were measured using an equipment of H₂ generation.The main results are concluded as following:Al-5Ti-1B refines Al grains of Al-Ga-In-Sn alloys more effectively compared to pure Ti.Grain refinement favors Al-water reaction of alloys,but Ti prohibits Al-water reactivities.The alloys exhibit the maximum H₂ generation rate as Al-5Ti-1B amount is 2.4 wt.%.Mg forms many kinds of compounds with Ga,In and Sn at Al grain boundaries,the types and amount of the compounds depend on Mg content of alloys.The Ga,In,Sn will precipitate from the anodic interfacial phases once the alloys are contacted with water,for the interfacial phases and Al matrix can form micro-galvanic cells.The dissolving of the anodic interfacial phases are connected with AVPD of different interfacial phases with respect to Al matrix and chemical bond type of interfacial phases.The content of Mg and Ga solute in Al lattice alters the electrical potential of AI matrix,hence it alters the AVPD of different interfacial phases with respect to Al matrix.The AVPD of interfacial phases of Mg-bearing alloys is related to the energy density of s-like state of those phase crystals.The absolute AVPD values of interfacial phases follow the order of Mg₂Sn>MgIn>MgzGa>Mg₅Ga₂,consistent with the reduction of energy density of s-like state?EDS?of those phase crystals.The dissolving difficulty of interfacial phases follows the order of Ga-bearing compound>Mg₂Sn>MgIn,which is determined by the strength of chemical bond and EDS of crystal phases.MgGa is very difficult to dissolve due to its stronger chemical bond and lowest EDS;Mg₂Sn is easier to dissolve due to its strongest chemical bond and highest EDS;but MgIn is easiest to dissolve due to its weakest chemical bond and higher EDS.Although MgGa is very difficult to dissolve,a slight of In added in alloy favors the precipitation of Ga from MgGa.Ga,In and Sn precipitate from the anodic interfacial phases as the interfacial phases corrode in water.Those low melting point metals will form Ga-In and Ga-In-Sn phases at Al grain boundaries.The alloy can continue to react with water by means of these new phases,exhibiting a different reaction mechanism from quaternary A 1-Ga-In-Sn alloy.The Mg-bearing alloys with Mg content above 4 wt.%show a lower H₂ generation rate and yield compared with those of Mg-bearing alloys with Mg content below 4 wt.%,because of the difficulty of Ga and In precipitation from MgsGa2-xInx and Mg₂Ga_1-xInx compared to from MgGa,MgGa₂ and MgIn.Cu does not form compounds with low melting point metals,but Cu solute in Al grains and CuAl₂ at Al grain boundaries reduce the H₂ generation rate and yield of alloys.Heat treatment changes the amount and type of interfacial phases together with content and amount of solutes and compounds in Al grains.As a result,it influences the the H₂ generation rate and yield of alloys.The above studies clearly show the mechanism of Al-water reaction of dissolvable aluminium alloys.The reasonable additions of many elements in alloys are found.The influences of heat treatment on microstructure and Al-water reactivities of alloys are grasped.These researches lay experimental bases for optimizing the comprehensive properties of dissolvable aluminium alloys.