• International Journal of Automotive Technology
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• v.7 no.5
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• pp.579-584
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• 2006

Aluminum Resistance Spot Weld(Al RSW) is an enabling technology for body assembly of low mass fraction vehicles. Due to the unreliable durability of spot-welded joints, applications of Al RSW are limited. This study presents experimental investigation on the use of a post-weld cold working process to improve the fatigue strength of Al RSW. The post-weld cold working process includes special shaped indenters that are pressed or driven into the structure to induce compressive residual stresses. The mechanical properties of the post-weld cold worked Al RSW were investigated, including the experimental results of fatigue and micro-hardness tests. Comparisons of the mechanical properties and qualitative results between the as-welded RSW specimens and the post-weld cold worked RSW specimens are discussed. The post-weld cold worked Al RSW samples had an increase in both microhardness and fatigue life.

• Korean Journal of Metals and Materials
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• v.49 no.1
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• pp.9-16
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• 2011

To develop a 6061 aluminum alloy with low residual stress and high tensile strength, a cryogenic treatment process was investigated. Compared to the conventional heat treatment process for precipitation hardening with artificial aging, the cryogenic treatment process has two additional steps. The first step is cryogenic quenching of the sample into liquid nitrogen, the second step is up-hill quenching of the sample into boiling water. The residual stress for the sample was measured by the $sin^2{\psi}$ method with X-ray diffraction. The 6061 aluminum alloy sample showed 67% relief in stress at the cryogenic treatment process with artificial aging at $175^{\circ}C$. From this study, it was found that the optimum cryogenic treatment process for a sample with low residual stress and high tensile strength is relatively low cooling speed in the cryogenic quenching step and a very high heating speed in the up-hill quenching step.

• Journal of the Korean Society for Heat Treatment
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• v.19 no.1
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• pp.20-29
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• 2006

Wear behaviour of B.390 aluminum alloy with different particle sizes of primary Si against a SM45C counterface was studied as a function of wear load and sliding velocity, using pin-on-disk apparatus under dry condition. The wear rate of specimen with fine primary Si particles showed increased wear resistance at high wear load, on the other side wear resistance of coarse primary Si particle size was improved at low wear load. As the compressive residual stress in the matrix increased remarkably by liquid nitrogen(LN) treatment, wear resistance of the LN treated specimen was more excellent than that of T6 treated specimen.

• Proceedings of the KIEE Conference
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• 1998.07g
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• pp.2521-2523
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• 1998

Freestanding flexible microstructures fabricated from deposited thin films become mechanically unstable when internal stresses exceed critical values. The residual stress and stress gradient of aluminum thin film were examined to make sure of fabricating the reproduceable aluminium structure. For good shape of micro mirror array and microstructures, the experiment was done varying thickness and deposition rate. As the aluminium film thickness increased from 0.8${\mu}m$ to 1.6${\mu}m$, the stress gradient decreased from 11.62MPa/${\mu}m$ to 2.62MPa/${\mu}m$. The residual stress values are from 42.4MPa to 62.24MPa of tensile stresses.

• Journal of Welding and Joining
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• v.5 no.1
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• pp.42-56
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• 1987

Fatigue Fracture behaviors of the TIG-welded aluminum alloys, such as Al 2024-T4, A1 5050-0 and Al 7075-T7 were investigated when a crack propagated from tensile residual stress region and compressive residual stress region. The experimental values were compared with the values expected by the Forman equation. The experimental results are summarized as the following: (1) In case of fatigue crack propagation from residual stress region, the values predicted by Forman equation were Found to exactly corresponded to the experimental values. (2) When the stress intensityfactors affected by compressive residual stress, Kres, were greater than the stress intensity factors by minimum applied stresses. Kmin, the Forman equation was found to be improper to be applied directly, but the equation appeared to be proper, if the stress ratio was modified to zero. (3) The experimental results confirmed that residual stress was relaxed by repeated tensile loading and the relaxing trend was greater in case of compressive residual stress than that of tensile residual stress.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.11
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• pp.1381-1389
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• 2012

The object of this study considers corrosion fatigue improvement of 7075-T6 aluminum by using shot peening treatment on 3.5% NaCl solution at room temperature. Aluminum alloy is generally used in aerospace structural components because of the light weight and high strength characteristics. Many studies have shown that an aluminum alloy can be approximately 50% lighter than other materials. Mostly, corrosion leads to earlier fatigue crack propagation under tensile conditions and severely reduces the life of structures. Therefore, the technique to improve material resistance to corrosion fatigue is required. Shot peening technology is widely used to improve fatigue life and other mechanical properties by induced compressive residual stress. Even the roughness of treated surface causes pitting corrosion, the compressive residual stress, which is induced under the surface layer of material by shot peening, suppresses the corrosion and increases the corrosion resistance. The experimental results for shot peened specimens were compared with previous work for non treated aluminum alloy. The results show that the shot peening treatment affects the corrosion fatigue improvement of aluminum alloys and the induced compressive residual stress by shot peening treatment improves the resistance to corrosion fatigue.

• Journal of Korea Foundry Society
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• v.29 no.5
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• pp.204-212
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• 2009

The effects of addition of magnesium only and the simultaneous addition of magnesium and aluminum on the graphite morphology of the cast iron with the composition of 3.6wt.% and 2.5wt.%Si poured into shell stack mold were investigated. The nodularity and mechanical properties of the specimen with smaller cross-section were higher than those with langer one, when copper was not added. When the magnesium only was added, the nodularity was decreased with decreased residual magnesium content and the C. V, graphite was obtained with the magnesium content in the range of 0.010~0.015wt.%. When the magnesium and aluminum were added together, the nodularity was decreased with decreased residual magnesium and increased aluminum contents. When copper was added, the volume fraction of pearlite in the matrix, strength and hardness were higher and elongation was lower for specimen with smaller cross-section. The volume fraction of pearlite, strength and hardness were increased and the elongation was decreased with increased copper content for the specimen with C, V, graphite.

• Journal of the Korean institute of surface engineering
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• v.29 no.2
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• pp.100-108
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• 1996

The internal stress of acidic electroless nickel deposits on zincated aluminum was determined by spiral contractometer. Several plating conditions such as inhibitor and complexing agent concentrations and pH affecting the internal stress were studied. The resulting intrinsic stress contribution to the total stress was discussed in terms of phosphorous content of the deposit, solution pH, and surface morphology. However, the most important was found to be thermal stress for the total stress of Al substrate, because of high thermal expansion coefficient of the aluminum substrate.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.438-444
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• 2003

A new method to measure residual stress in micron and nano scale films is described. In the theory it is based on Linear Elastic Fracture Mechanics. And in the techniques it depends on the combined capability of the focused ion beam (FIB) imaging system and of high-resolution digital image correlation (DIC) software. The method can be used for any film material (whether amorphous or crystalline) without thinning the substrate. In the method, a region of the film surface is highlighted and scanning electron images of that region taken before and after a long slot, depth a, is introduced using the FIB. The DIC software evaluates the displacement of the surface normal to the slot due to the stress relaxation by using features on the film surface. To minimize the influence of signal noise and rigid body movement, not a few, but all of the measure displacements are used for determining the real residual stress. The accuracy of the method has been assessed by performing measurements on a nano film of diamond like carbon (DLC) on glass substrate and on micro film of aluminum oxide thermally grown on Fecrally substrate. It is shown that the new method determines the residual stress ${\sigma}_R=-1.73$ GPa for DLC and ${\sigma}_R=-5.45$ GPa for the aluminum oxide, which agree quite well with ones measured independently.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.99-100
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• 2006

Cold gas dynamic spray or cold-spray is a deposition process, which causes deformation of a thin substrate. The deformation is usually convex to the deposited side. In this research, the main cause of the deformation was investigated using 6061-T6 aluminum alloy. The effects or anisotropic coefficient or thermal expansion (CTE) or the deposited layer by cold-spray and residual stress were studied by experiments and finite element analysis. The Hole Drilling method was applied to measure residual stress in the cold-spray layer and substrate. The data obtained by the experiments were used for the analysis of substrate deformation. From the result of the analysis, it was concluded that compressive residual stress was the main reason of substrate deformation while CTE had little effect.