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岸, 陽一 ; 広瀬, 幸雄 ; 佃, 市三 ; 永井, 滋一 ; 東, 健司
概要:
金沢大学大学院自然科学研究科<br />Tensile properties and stress corrosion cracking (SCC) resistance of Al-8 wt.% Zn-1 wt.% Mg system a
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lloys with various Cu and La contents were investigated.The influences of additional elements on mechanical properties and SCC life were discussed on the basis of experimental results.The results obtained in the present work are as follows;(1) Additions of elements of Cu and La were effective to decrease the grain size of those materials.In particular,the grain sizes in alloys containing La contents of more than 1.7 wt.% were small at 20μm,comparing with that in the master alloy.(2) For the present alloys containing La,the second phase particles,consisting of Zn and La,have the capacity of hydrogen storage.These particles were between 5 and 10μm in size,and were dispersed in the matrix bomogeneously.(3) Tensile properties were improved with increasing Cu or La content.For the alloys with Cu and La,the tensile strength was from 450 to 500 Mpa,and the elongation between 14 and 17%.(4) The alloys containing La had high resistance to SCC.Their SCC lives were about 15 times as long as that of the master alloy.In conclusion,the alloys added Cu more than 0.6 wt.% and La 4.0 wt.% were much superior to the master alloy in both the tensile properties and the SCC resistance.
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岸, 陽一 ; 広瀬, 幸雄 ; 佃, 市三 ; 永井, 滋一 ; 東, 健司
概要:
金沢大学大学院自然科学研究科<br />The effects of addition of Zr on both microstructures and mechanical properties of four advanced Ak-
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8 wt.% Mg-0～2.4 wt.% La alloys were investigated, which had excellent stress corrosion cracking (SCC) resistance. The main results are as follows ; (1) The peripheral zone of all the extruded Al-Zn-Mg-Zr-La alloys were recrystallized with coarse grained structures, and the regions within the core were fibrous and unrecrystallized on macroscale. The core region was consisted of subgrains with low angle orientation, which were situated in layer-like colonies. For the alloys with La, the primary phase particles including elements of La and Zn dispersed in the matrix. (2) Tensile properties of Al-8 wt.% Zn-1 wt.% Mg-0.1 wt.% Zr with various La content were much superior to Al-8 wt.% Zn-1 wt.% Mg alloy (the master alloy). Values in tensile strength were from 460 to 490 MPa, and a maximum in elongation was about 11%. (3) The crack nucleation life on the SCC tests increased with increasing La content. The core region including the fibrous structures with fine subgrains exhibited more resistant to SCC than the peripheral one with the recrystallized coarse structure.
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岸, 陽一 ; 広瀬, 幸雄 ; 佃, 市三 ; 永井, 滋一 ; 東, 健司
概要:
金沢大学大学院自然科学研究科<br />Two groups of the extruded high strength Al-Zn-Mg-Cu-La system alloys, including Al-10 wt.%Zn-1 wt.%
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Mg-1.5 wt.%Cu-3 wt.%La with various Cr and Mn contents and Al-8 wt.%Zn-1.2 wt.%Cu-4.0 wt.%La with various Mg contents, were with developed as the mechanical materials a good stress corrosion cracking(SCC)resistance. In these alloys, the effects of the additional elements were investigated on the mechanical properties and SCC life. The main results are as folows ; (1)The second phase particles which contained Zn and La were observed in the matrix, and dispersed homogeneously. The size of the particles was 5 to 10 μm. For the alloys with Cr, dispersoids including Cr were also observed in the matrix. Their size was over 10 μm. (2)The maximum value of 568 MPa in tensile strength was observed in Al-8 wt.%Zn-1.2 wt.%Cu-4.0 wt.%La with 2.5 wt.%Mg, which was nearly equal to the commercial aluminum alloys-7075-T73 and 7475-T6. (3)The excellent resistance of SCC was obtained in these alloys. Their SCC lives were over 15 times as long as that of Al-8 wt.%Zn-1 wt.%Mg master alloy. In conclusion, we developed extruded Al-high Zn-low Mg system alloys with high strength and good SCC resistance.
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岸, 陽一 ; 広瀬, 幸雄 ; 佃, 市三 ; 永井, 滋一 ; 東, 健司
概要:
金沢大学大学院自然科学研究科<br />Extruded Al-8 wt.%Zn-1～2.5 wt.%Mg-1.2 wt.%Cu-4 wt.%La alloys with high tensile strength and good str
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ess corrosion cracking resistance were developed and their fracture toughness was investigated. The effect of metallurgical parameter on the fracture toughness value was examined. The main results are as follows ; (1) The fracture toughness values of the extruded Al-8 wt.%Zn-1～2.5 wt.%Mg-1.2 wt.%Cu-4 wt.%La, which were about 20 MPa√<m> without anisotropy, were not influenced by Mg content. (2) The second phase particles in the extruded alloys, which consisted of Zn and La, were estimated quantitatively. The mean diameter was about 4.7 μm and the volume fraction of the particles was 1.6～2.3 vol.%. (3) The second phase particles consisting of Zn and La in the extruded alloys cracked easily, and became the nucleus of voids when the matrix fractured. The fracture toughness of the extruded alloys was affected by the particles. The fracture toughness value, K_<IC>was related to the volume fraction of the second phase particles, f_V, and the mean diameter of the particles, D, as follows: K_<IC>┤[ζσ_<0.2>E(π/6)^<1/3>D]^<1/2>・f^<-1/6>_V∝(DEσ_<0.2>)^<1/2>・f^<-1/6>_V where ζ is constant, σ_<0.2> is 0.2% proof stress and E is Young's modulus.
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岸, 陽一 ; 広瀬, 幸雄 ; 佃, 市三 ; 永井, 滋一 ; 東, 健司
概要:
金沢大学大学院自然科学研究科<br />Fatigue crack growth tests on an extruded Al-8 wt.% Zn-2.5 wt.% Mg-1.2 wt.% Cu-4 wt.% La alloy were
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carried out using CT specimens(TL orientation). Crack closure was examined by the unloading elastic compliance technique. The main results are as follows; (1)The effect of stress ratio was observed on the crack growth rate, da/dN, vs.stress intensity factor range, ΔK, diagram. A higher stress ratio gives a faster crack growth rate at same ΔK. (2)Crack closure was observed under the stress ratio=0.1, and its degree was increasing with decreasing stress intensity factor range. On the other hand, it was not at the stress ratio=0.5. (3)The effect of stress ratio on the second region of da/dN vs.ΔK diagram disappeared when the effective stress intesity factor range, ΔK_<eff> was used instead of ΔK. (4)The second region of da/dN vs.ΔK_<eff> diagram for the extruded Al-8 wt.% Zn-2.5 wt.% Mg-1.2 wt.% Cu-4 wt.% La alloy was in agreement with that for the commercial 7075T6 alloy. So, the fatigue crack growth resistance of the extruded Al-8 wt.% Zn-2.5 wt.% Mg-1.2 wt.% Cu-4 wt.% La alloy is nearly equal to that of the commercial 7075T6 alloy.
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