Structures And Properties Of The High Strength Aluminum Alloys And High Entropy Alloys

Al alloys have received considerable attention due to their low density and highspecific strength. As Al is fcc structure, it has good plasticity and toughness too.Furthermore it has good property of casting, processing work and cutting, it can bemade semi product.With the development of science technology, the trend ofautomobiles industry is gradually face to safe, environmental and economize. One ofthe most important applications is alleviate automobile dead weight by use of Alalloys.In present, there are several methods to improve strengthen as follows: 1,Alloying: Via adding Cu, Zn, Mg etc alloy elements to improve alloy intension;2,Molding;3, amorphouzation, including amorphous phase or nanometer phase;nano-scale compounds particles or norm crystal phase attached in the α-Almatrix.In this thesis, we choose AlxLaNiTiMn with study object and melte in avacuum arc furnace under argon atmosphere, we use rapid solidification technologyto obtain the alloy, the x is 80,85,90.With analyzing, we find the alloy base on the α-Al matrix and intermetalliccompounds (La3All1,Al2Mn3,Al3Ti,NiTi) in the α-Al matrix. When the content ofAl increase, intermetallic compounds decrease, content of α-Al enlarges, its particlesize becomes smaller, the alloy's hardness and compress strength decrease, but wearresistant is better.When the content of Al is 80% in the alloy, the hardness of alloy is 577HV, butwhen the content of Al is 90%, the hardness is 285HV, and compress strength ofalloy is from 904Mpa to 710Mpa.In the middle of 2004, the notion of high entropy alloy is formally proposed.Based on the high entropy alloy theory and traditional smelting technology, we fatherstudy the property of high entropy alloy.High entropy alloy is composed by varies elements with nearly the same molarratio in order to form the single solid solution.The theory of high entropy come from Boltzmann's hypothesis on therelationship between entropy and system complexity, the configurational entropychange per mole, ΔSconf, during the formation of a solid solution from n elementswith equimolar fractions may be calculated from the following equation:ΔSconf=-klnw=-R(1/nln1/n+1/nln1/n+…1/nln1/n)=-Rln1/n=Rlnnwhere k is Boltzmann's constant, w is the number of ways of mixing, and R is the gasconstant: 8.314 J/Kmole. For example, when n is 5, the ΔSconf is 1.618R, larger thanthat of metal fusion.We study the alloy property of AlTiNiMnBx, CuCoNiCrFe, CuMoNiCrFe,CuAl0.5NiCrFe, AlCoNiCrFe, AlNiTiCuCrSi alloys.In the study, we find that the peaks of x-ray diffraction become weak, whilecrystal lattice parameters, hardness and densities increase when the content fractionof B element increases from 0.1 to 0.5. Taking the sample AlTiNiMnB0.5 as anexample, we find that the sample begins to melt at about 1050℃ through the DSCanalysis. Therefore, it can be considered that the kind of alloy is highlythermodynamic stabilization.After studying the alloys of CuCoNiCrFe, CuMoNiCrFe, CuAl0.5NiCrFe,AlCoNiCrFe, AlNiTiCuCrSi, we find that the peaks of x-ray diffraction are mainlyFCC structure without Al element, and the peaks become FCC+BCC structure withthe presence of Al, while the structure is mainly BCC structure without Cu element.Thus, BCC structure ascribes to Al, while FCC structure ascribing to Cu. When thecomposition of alloys vary from CuCoNiCrFe, CuAl0.5NiCrFe, AlCoNiCrFe toAlNiTiCuCrSi, the binding energies and the lattice deformations increase, and thesolid solutions are enhanced. Taking the sample CuAl0.5NiCrFe and AlCoNiCrFe asan example, we find that the samples' compress strength increase, the compressstrength of them are 1392Mpa and1454Mpa.