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A comparison of welding techniques was performed to determine the most effective method for producing aluminum tailor-welded blanks for high volume automotive applications. Aluminum sheet was joined with an emphasis on post weld formability, surface quality and weld speed. Comparative results from several laser based welding techniques along with friction stir welding are presented. The results of this study demonstrate a quantitative comparison of weld methodologies in preparing tailor-welded aluminum stampings for high volume production in the automotive industry. Evaluation of nearly a dozen welding variations ultimately led to down selecting a single process based on post-weld quality and performance.

Fatigue behavior of aluminum alloys under multiaxial loading was investigated with both cast aluminum A356-T6 and wrought alloy 6063-T6. The dominant multiaxial fatigue crack preferentially nucleates from flaws like porosity and oxide films located near the free surface of the material. In the absence of the flaws, the cracking/debonding of the second phase particles dominates the crack initiation and propagation. The number of cracked/debonded particles increases with the number of cycles, but the damage rate depends on loading paths. Among various loading paths studied, the circle loading path shows the shortest fatigue life due to the development of complex dislocation substructures and severe stress concentration near grain/cell boundaries and second phase particles.

The impact of texture on r-value and its measurement in magnesium alloy sheets has been studied using digital image correlation and electron backscatter diffraction techniques. Two magnesium alloy sheets with distinct textures were used in the present study, namely, AZ31 with a strong basal texture and ZE21 with a randomized texture. It is well known that a conventionally processed AZ31 magnesium sheet has strong basal texture, necessitating contraction and double twinning to accommodate thinning strain. The strain distribution on the sheet surface evolves nonlinearly with strain, impacting the measured r-value. In particular, the normal approach to measuring r-value based on average strains over the gauge section leads to the erroneous conclusion that r-value increases with deformation. When the r-value is measured locally at any point inside or outside the neck, the r-value is shown to have a constant value of 3 for all strain values.

Advanced high strength steels (AHSS) offer a good balance of strength, durability, crash energy absorption and formability. Applications of AHSS for lightweight designs of automotive structures are accelerating in recent years to meet the tough new CAFE standard for vehicle fuel economy by 2025. At the same time, the new generation pickup cargo box is to be designed for a dramatic increase in payload. Upgrading the box material from conventional mild steels to AHSS is necessary to meet the conflicting requirements of vehicle light weighting and higher payload. In this paper, typical AHSS grades such as DP590 and DP780 were applied to selected components of the pickup cargo box for weight reduction while meeting the design targets for fatigue, strength and local stiffness.

Forming a metal gainer is a common technique used to gather material in a high stretch region along an edge in preparation for a subsequent flanging operation. This technique has proven to be successful for mild steels, but needs to be evaluated for the applicability to advanced high strength steels (AHSS). The Auto/Steel Partnership High Strength Stamping Team launched a project for this study. Experimental trials were conducted on gainer forming, trimming and flanging. Twelve (12) AHSS have been tested with tensile strengths ranging from 460 to 1240 MPa. Edge stretch limits for flanging have been evaluated and compared to flanging without gainers. Different trimming and flanging approaches have also been tried. The results show that metal gainers are not advantageous for flanging of higher strength AHSS.

This paper presents a technological comparison of weldability and mechanical properties between a dual phase steel (DP) and an advanced high strength low alloy steel (AHSLA) used for automotive structural parts in order to demonstrate some unclear characteristics of each. Samples were spot welded and had their hardness and microstructure analyzed, also a shear test was applied on the weld button area. The edge stretchability was analyzed using hole expansion tests and tensile tests to determine the tensile and yield strength, anisotropic coefficients and total elongation. Data were used to estimate crash energy absorption. The results showed an AHSLA steel with higher than typical ductility. Finally, while DP showed improved stretchability, it was also concluded that such AHSLA could perform better bendability, drawability, flangeability and weldability.

Edge fracture is one of the major issues for stamping Advanced High Strength Steel (AHSS). Recent studies have showed this type of fracture is greatly affected by an improper trimming process. The current production trimming process used for the conventional mild steels has not been modified for AHSS trimming. In addition to the high-energy requirement, the current mechanical trimming process would generate a rough edge (burr) with microcracks in trimmed edges for AHSS trimming, which could serve as the crack initiation during forming. The purpose of this study is to develop a proper production trimming process for AHSS and elucidate the effect of the trimmed edge conditions on edge fracture. A straight edge shearing device with the capability of adjusting the shearing variables is used in this study.

Global regulations intended to enhance pedestrian protection in a vehicle collision, thereby reducing the severity of pedestrian injuries, are presenting significant challenges to vehicle designers. Vehicle hoods, for example, must absorb a significant amount of energy over a small area while precluding impact with a hard engine compartment component. In this paper, a simple passive approach for pedestrian protection is introduced in which thin metal alloy sheets are bent to follow a C-shaped cross-sectional profile thereby giving them energy absorbing capacity during impact when affixed to the underside of a hood. Materials considered were aluminum (6111-T4, 5182-O) and magnesium (AZ31-O, AZ61-O, ZEK100) alloys. To evaluate the material effect on the head injury criterion (HIC) score without a hood, each C-channel absorber was crushed in a drop tower test using a small dart.

Heat treated cast aluminum components like engine blocks and cylinder heads can develop significant amount of residual stress and distortion particularly with water quench. To incorporate the influence of residual stress and distortion in cast aluminum product design, a rapid simulation approach has been developed based on artificial neural network and component geometry characteristics. Multilayer feed-forward artificial neural network (ANN) models were trained and verified using FEA residual stress and distortion predictions together with part geometry information such as curvature, maximum dihedral angle, topologic features including node's neighbors, as well as quench parameters like quench temperature and quench media.

Advanced high strength steels (AHSS) are widely used in the automotive industry for various applications especially for structural and safety parts. One of the concerns for AHSS in stamping operations is edge fracture originating from sheared blanked edges. This type of failure cannot be predicted by computer simulations using the conventional forming limit as the failure criterion. The reason for this is that edge damage produced by the blanking operation is not incorporated into the computer models to properly simulate the material edge formability. This study presents a method to evaluate edge damage in terms of the residual stress at the sheared edge produced by the blanking operation. The method uses the level and distribution of edge strain hardening (ESH) through the material thickness as an index to characterize the edge damage caused by the shearing operation.

Edge flanging represents one of the forming modes employed in multistage forming, and advanced high strength steels (AHSS) are more prone to edge cracking during sheared edge flanging than the conventional high strength steels (HSS) and mild steels. The performance of the sheared edge in flanging operation depends on the remaining ductility of the material in the sheared edge after the work hardening (WH) and damage produced by blanking and subsequent forming operations. Therefore, it is important to analyze the effect of work hardening produced by blanking and subsequent forming operations prior to edge flanging on the edge flanging performance. In this study, the effect of different forming operation sequences prior to edge flanging on the edge flanging performance was analyzed for a dual phase 780 steel.

In August 2005, National Highway Traffic Safety Administration (NHTSA) proposed to increase the roof strength requirement under Federal Motor Vehicle Safety Standard (FMVSS) 216 from 1.5 to 2.5 times unloaded vehicle weight (UVW). To meet the new requirement with a minimum impact on vehicle weight and cost, the automotive community is working actively to develop improved roof architectures using advanced high strength steels (AHSS) and other lightweight materials such as structural foam. The objective of this study is to develop an optimized steel-only solution with low material and part-manufacturing costs. Since the new regulation will present a particular challenge to the roof architectures of large vans, pickup trucks and SUVs due to their large mass and size, a validated roof crush model on a B-Pillar-less light truck is utilized in this study.

More Mg alloys are being considered for uses in the automotive industry. Since the corrosion performance of Mg alloy components in practical service environments is unknown, long term corrosion testing at automotive proving grounds will be an essential step before Mg alloy components can be implemented in vehicles. However, testing so many Mg alloy candidates for various parts is labor intensive for the corrosion engineers at the proving grounds. This report presents preliminary results in evaluating corrosion performance of Mg alloys based on rapid corrosion and electrochemical tests in the lab. In this study, four Mg alloy candidates for transmission cases and oil pans: AE44, AXJ530, MRI153M and MRI230D were tested in the lab and at General Motors Corporation Milford Proving Ground and their corrosion results were compared.

To improve the energy absorption capacity of front-end structures during a vehicle crash, a novel 12-sided cross-section was developed and tested. Computer-aided engineering (CAE) studies showed superior axial crash performance of the 12-sided component over more conventional cross-sections. When produced from advanced high strength steels (AHSS), the 12-sided cross-section offers opportunities for significant mass-savings for crash energy absorbing components such as front or rear rails and crush tips. In this study, physical crash tests and CAE modeling were conducted on tapered 12-sided samples fabricated from AHSS. The effects of crash trigger holes, different steel grades and bake hardening on crash behavior were examined. Crash sensitivity was also studied by using two different part fabrication methods and two crash test methods. The 12-sided components showed regular folding mode and excellent energy absorption capacity in axial crash tests.

AZ31B Mg sheet is being considered for automotive applications. This study investigates the effect of pre-treatments, such as heat-treatments and surface treatments, on the corrosion performance of AZ31B sheet, with a goal of learning which pre-treatment can improve corrosion resistance of the sheet material in production. It is found that the heat-treatment and oxidation during a warm and hot forming (WHF) process will not deteriorate the corrosion performance of the AZ31B sheet; polishing and acid etching can clean the surface and significantly increase the corrosion resistance, but corrosion can be accelerated by sandblasting which contaminates the surface. The change in corrosion performance can be associated with surface cleaning or contamination of the sheet by these pre-treatments. Furthermore, the influence of a pre-treatment on the uncoated AZ31B sheet may affect its corrosion behavior after coating.

One of the concerns for advanced high strength steels (AHSS) in stamping operations is the failure of sheared edges in stretching modes. When a forming operation requires stretching edges, local formability becomes a very important factor of the material application, particularly for the AHSS. The local formability of a material is usually characterized by the hole expansion ratio (HER). During edge stretching, the sheared edge can be in contact with the tool or it can be free. These two conditions can be simulated by the hole expansion (HE) test using a conical punch and a flat bottom punch, respectively. In this study, the local formability of a dual phase (DP) 780 steel is evaluated using the HE test. The hole expansion tests were performed using a digital record and measurement system (DRMS) which allows the measurement of the final diameter of the hole at the moment of a localized fracture or a through-thickness crack at the hole edge.

Magnesium alloys are not corrosion resistant in many applications and they require coating protection. In this study, we developed an electroless E-coating technique for magnesium alloys and discussed a cathodic E-coating deposition mechanism for the electroless E-coating process. This coating can be formed within a few seconds by dipping a magnesium alloy (i.e., AZ91D) in an E-coat bath without applying a current or voltage. The deposited electroless coat can offer good protection to the AZ91D magnesium alloy in 5 wt% NaCl corrosive solution as well as in a phosphating bath. The most interesting finding is that the electroless coating is not sensitive to local damage. No preferential corrosion attack occurred along the scratches made on the coating.

A methodology that enables two-dimensional strain field measurement in the vicinity of ductile rupture is described. Fully martensitic steel coupons were strained to fracture using a miniature tensile stage with custom data and image acquisition systems. Rupture initiated near the center of each coupon and progressed slowly toward the gage section edges. A state-of-the-art digital image correlation technique was used to compute the true strain field before rupture initiation and ahead of the resulting propagating macroscopic crack before final fracture occurred. True strains of the order of 95% were measured ahead of the crack at later stages of deformation.