http://doras.dcu.ie/17608/1/Final_Version%2C_Review_paper.pdf

Optimization of different welding processes using statistical and numerical approaches - A reference guide

Spot welding, particularly resistance spot welding (RSW), is a critical joining process in automotive industry. The development of advanced high strength steels for applications in automotive industry is accompanied with a challenge to better understand the physical and mechanical metallurgy of these materials during RSW. The present paper critically reviews the fundamental understanding of structure–properties relationship in automotive steels resistance spot welds. The focus is on the metallurgical characteristics, hardness–microstructure correlation, interfacial to pullout failure mode transition and mechanical performance of steel resistance spot welds under quasi-static, fatigue and impact loading conditions. A brief review of friction stir spot welding, as an alternative to RSW, is also included.

Critical review of automotive steels spot welding: process, structure and properties

Failure mode of resistance spot welds is a qualitative indicator of weld performance. Two major types of spot weld failure are pull-out and interfacial fracture. Interfacial failure, which typically results in reduced energy absorption capability, is considered unsatisfactory and industry standards are often designed to avoid this occurrence. Advanced High Strength Steel (AHSS) spot welds exhibit high tendency to fail in interfacial failure mode. Sizing of spot welds based on the conventional recommendation of 4t0.5 (t is sheet thickness) does not guarantee the pullout failure mode in many cases of AHSS spot welds. Therefore, a new weld quality criterion should be found for AHSS resistance spot welds to guarantee pull-out failure. The aim of this paper is to investigate and analyze the transition between interfacial and pull-out failure modes in AHSS resistance spot welds during the tensile–shear test by the use of analytical approach. In this work, in the light of failure mechanism, a simple analytical model is presented for estimating the critical fusion zone size to prevent interfacial fracture. According to this model, the hardness ratio of fusion zone to pull-out failure location and the volume fraction of voids in fusion zone are the key metallurgical factors governing type of failure mode of AHSS spot welds during the tensile–shear test. Low hardness ratio and high susceptibility to form shrinkage voids in the case of AHSS spot welds appear to be the two primary causes for their high tendency to fail in interfacial mode.

Failure mode transition in AHSS resistance spot welds. Part I. Controlling factors

Quasi-static tensile shear mechanical properties of resistance spot welds of three dual phase (DP) grades including DP600, DP780 and DP980 are investigated. Results showed that weld fusion zone size, failure mode and the strength/ductility of failure location are the main factors governing the peak load and the energy absorption of spot welds. Heat affected zone (HAZ) softening plays an important role in mechanical properties of DP steels with higher volume fraction of martensite (i.e. DP780 and DP980). It was shown that the peak load of the spot welds is not proportionally correlated to the tensile strength of the base metal. Pronounced HAZ softening in DP980 resulted in reducing its tendency to fail in interfacial failure mode in comparison to DP780. In addition, despite its lower base metal ductility, DP980 weld exhibits enhanced ductility and energy absorption than DP780 due to its pronounced HAZ softening.

Key factors influencing mechanical performance of dual phase steel resistance spot welds

Influence of fusion zone size and failure mode on mechanical performance of dissimilar resistance spot welds of AISI 1008 low carbon steel and DP600 advanced high strength steel

A crush rail or other structural member of a vehicle is provided with crush triggers. The crush triggers are formed by heating localized areas of the crush rail or other part and allowing them to cool slowly to provide increased ductility and reduced strength in a localized region. The crush rail is designed to collapse in a series of convolutions in a regular and repeated pattern. Crush triggers may be provided on body pillars, steering columns, drive shafts, engine support cradles, and other parts of a vehicle. A plurality of crush triggers may be provided on a single structural member depending upon impact absorption requirements.

Method of improving impact absorbing and deformation control characteristics of vehicle components

A method of bonding a thermally sprayed coating to a non-roughened light metal (i.e. cast aluminum-based) surface. The method comprises the steps of (a) depositing a flux material (i.e. potassium aluminum's fluoride containing up to 50 molar % other fluoride salts) onto such cast surface which has been cleansed to be substantially free of grease and oils, such deposition providing a dry flux coated surface, the flux being capable of removing oxide on the cast surface and having a melting temperature below that of the cast surface; (b) thermally activating the flux in the flux coated surface to melt and dissolve any oxide residing on the cast surface; and (c) concurrently therewith or subsequent to step (b) thermally spraying metallic droplets or particles onto the flux coated surface to form a metallic coating that is metallurgically bonded to the cast surface.

Method of bonding thermally sprayed coating to non-roughened aluminum surfaces

A method of thermally spraying a coating onto the interior of a cylindrical surface which coating is graded between enhanced optimal machinability and enhanced wear resistance. The method comprises the steps of; (a) preparing a cylindrical bore surface of a light metal substrate cleansed of grease and oils and modified to alter any oxide film present thereon; (b) thermally spraying a deposit of metallic droplets or particles onto the prepared bore surface using metal wire or powder feedstocks (low carbon steel or stainless steel) and a primary atomizing gas that projects the droplets or particles as a spray, the droplets or particles having a chemistry capable of metallurgically bonding with the metal of the substrate, the spray being positioned to lay down a generally uniform coating of such droplets or particles; and (c) varying the chemical content of the atomizing gas in two or more stages to proceed from essentially a metal droplet oxide-forming gas (air or oxygen) to essentially an inert or non-oxidizing gas (nitrogen or argon) relative to the droplets or particles.

Method of depositing a thermally sprayed coating that is graded between being machinable and being wear resistant

Key factors that contribute to the formation of shrinkage voids in resistance spot welds of advanced high-strength steels were investigated.

Reducing shrinkage voids in resistance spot welds

A method for fluxless brazing of unclad aluminum includes forming first and second components to be joined of unclad aluminum; etching selected surface areas of the components; depositing an elemental metal on the selected surface areas; abutting the first and second components along the etched surfaces forming a junction; applying an aluminum filler about the junction; and heating the components and filler and bonding the components and filler.

Armando Joaquin

Papers

Method of improving impact absorbing and deformation control characteristics of vehicle components

Method of bonding thermally sprayed coating to non-roughened aluminum surfaces

Method of depositing a thermally sprayed coating that is graded between being machinable and being wear resistant

Reducing shrinkage voids in resistance spot welds

Fluxless brazing of unclad aluminum using selective area plating